[pkg/ottl] Add complex indexing to paths and converters

[TylerHelmuth]

Description:
Adds support for complexing indexing to OTTL:

• Updates the grammar to support indexing the result of Converters and updates the Contexts
• Updates contexts to support indexing maps with multiple fields and setting nested map fields.

As discussed in the issue, this PR's initial stance is to include indexing of Converters. If during review we determine that capability is not worth it we can remove it and stick only with complex indexing of Paths.

This PR does not yet add the extra checking that Contexts should be doing to ensure there are no extraneous Keys/Fields in the path. They are already doing a poor job of that so I'll submit a future PR to clean all that up.

Link to tracking Issue:
Closes #16811

Testing:
Added unit tests

Documentation:
Updated READMEs to include use of multiple indexes

[runforesight]

Foresight Summary

    
Major Impacts

build-and-test duration(33 minutes 4 seconds) has decreased 13 minutes 45 seconds compared to main branch avg(46 minutes 49 seconds).

View More Details

⭕  build-and-test-windows workflow has finished in 7 seconds (30 minutes 36 seconds less than main branch avg.) and finished at 12th Apr, 2023.

---

Job	Failed Steps	Tests
windows-unittest-matrix	-     🔗	N/A	See Details
windows-unittest	-     🔗	N/A	See Details

---

✅  telemetrygen workflow has finished in 1 minute 9 seconds and finished at 12th Apr, 2023.

---

Job	Failed Steps	Tests
build-dev	-     🔗	N/A	See Details
publish-latest	-     🔗	N/A	See Details
publish-stable	-     🔗	N/A	See Details

---

✅  check-links workflow has finished in 1 minute 34 seconds (⚠️ 36 seconds more than main branch avg.) and finished at 12th Apr, 2023.

---

Job	Failed Steps	Tests
changed files	-     🔗	N/A	See Details
check-links	-     🔗	N/A	See Details

---

✅  changelog workflow has finished in 1 minute 41 seconds and finished at 12th Apr, 2023.

---

Job	Failed Steps	Tests
changelog	-     🔗	N/A	See Details

---

✅  prometheus-compliance-tests workflow has finished in 3 minutes 25 seconds (3 minutes less than main branch avg.) and finished at 12th Apr, 2023.

---

Job	Failed Steps	Tests
prometheus-compliance-tests	-     🔗	N/A	See Details

---

✅  e2e-tests workflow has finished in 10 minutes 52 seconds (3 minutes 13 seconds less than main branch avg.) and finished at 12th Apr, 2023.

---

Job	Failed Steps	Tests
kubernetes-test (v1.26.0)	-     🔗	N/A	See Details
kubernetes-test (v1.25.3)	-     🔗	N/A	See Details
kubernetes-test (v1.24.7)	-     🔗	N/A	See Details
kubernetes-test (v1.23.13)	-     🔗	N/A	See Details

---

✅  load-tests workflow has finished in 15 minutes 44 seconds (⚠️ 5 minutes 12 seconds more than main branch avg.) and finished at 12th Apr, 2023.

---

Job	Failed Steps	Tests
setup-environment	-     🔗	N/A	See Details
loadtest (TestIdleMode)	-     🔗	N/A	See Details
loadtest (TestBallastMemory|TestLog10kDPS)	-     🔗	N/A	See Details
loadtest (TestMetric10kDPS|TestMetricsFromFile)	-     🔗	N/A	See Details
loadtest (TestMetricResourceProcessor|TestTrace10kSPS)	-     🔗	N/A	See Details
loadtest (TestTraceNoBackend10kSPS|TestTrace1kSPSWithAttrs)	-     🔗	N/A	See Details
loadtest (TestTraceBallast1kSPSWithAttrs|TestTraceBallast1kSPSAddAttrs)	-     🔗	N/A	See Details
loadtest (TestTraceAttributesProcessor)	-     🔗	N/A	See Details

---

✅  build-and-test workflow has finished in 33 minutes 4 seconds (13 minutes 45 seconds less than main branch avg.) and finished at 12th Apr, 2023.

---

Job	Failed Steps	Tests
govulncheck	-     🔗	N/A	See Details
setup-environment	-     🔗	N/A	See Details
check-codeowners	-     🔗	N/A	See Details
checks	-     🔗	N/A	See Details
lint-matrix (receiver-0)	-     🔗	N/A	See Details
lint-matrix (receiver-1)	-     🔗	N/A	See Details
lint-matrix (processor)	-     🔗	N/A	See Details
lint-matrix (exporter)	-     🔗	N/A	See Details
lint-matrix (extension)	-     🔗	N/A	See Details
lint-matrix (connector)	-     🔗	N/A	See Details
lint-matrix (internal)	-     🔗	N/A	See Details
lint-matrix (other)	-     🔗	N/A	See Details
check-collector-module-version	-     🔗	N/A	See Details
build-examples	-     🔗	N/A	See Details
correctness-metrics	-     🔗	N/A	See Details
correctness-traces	-     🔗	N/A	See Details
integration-tests	-     🔗	N/A	See Details
unittest-matrix (1.20, receiver-0)	-     🔗	N/A	See Details
unittest-matrix (1.20, receiver-1)	-     🔗	N/A	See Details
unittest-matrix (1.20, processor)	-     🔗	N/A	See Details
unittest-matrix (1.20, exporter)	-     🔗	N/A	See Details
unittest-matrix (1.20, extension)	-     🔗	N/A	See Details
unittest-matrix (1.20, connector)	-     🔗	N/A	See Details
unittest-matrix (1.20, internal)	-     🔗	N/A	See Details
unittest-matrix (1.20, other)	-     🔗	N/A	See Details
unittest-matrix (1.19, receiver-0)	-     🔗	N/A	See Details
unittest-matrix (1.19, receiver-1)	-     🔗	N/A	See Details
unittest-matrix (1.19, processor)	-     🔗	N/A	See Details
unittest-matrix (1.19, exporter)	-     🔗	N/A	See Details
unittest-matrix (1.19, extension)	-     🔗	N/A	See Details
unittest-matrix (1.19, connector)	-     🔗	N/A	See Details
unittest-matrix (1.19, internal)	-     🔗	N/A	See Details
unittest-matrix (1.19, other)	-     🔗	N/A	See Details
lint	-     🔗	N/A	See Details
unittest (1.20)	-     🔗	N/A	See Details
unittest (1.19)	-     🔗	N/A	See Details
cross-compile (darwin, amd64)	-     🔗	N/A	See Details
cross-compile (darwin, arm64)	-     🔗	N/A	See Details
cross-compile (linux, 386)	-     🔗	N/A	See Details
cross-compile (linux, amd64)	-     🔗	N/A	See Details
cross-compile (linux, arm)	-     🔗	N/A	See Details
cross-compile (linux, arm64)	-     🔗	N/A	See Details
cross-compile (linux, ppc64le)	-     🔗	N/A	See Details
cross-compile (windows, 386)	-     🔗	N/A	See Details
cross-compile (windows, amd64)	-     🔗	N/A	See Details
build-package (deb)	-     🔗	N/A	See Details
build-package (rpm)	-     🔗	N/A	See Details
windows-msi	-     🔗	N/A	See Details
publish-check	-     🔗	N/A	See Details
publish-stable	-     🔗	N/A	See Details
publish-dev	-     🔗	N/A	See Details
rotate-milestone	-     🔗	N/A	See Details

---

🔎 See details on Foresight

^{*You can configure Foresight comments in your organization settings page.}

[evan-bradley]

Looks good to me overall. Nice work.

[TylerHelmuth]

@evan-bradley with the rebase the core logic changes now reside in expression.go (for Converters) and contexts/internal/map.go for Contexts. I was too zealous with my refactor in the other PR, not as much stuff needed to move 🤷

[evan-bradley]

Looks good to me. I think it would be a good move to have tests covering the error conditions when indexing, but I won't block on that.

[codeboten]

Please resolve the conflict