[cluster-agent] Fix CWS Instrumentation webhook label selector and error handling

[Gui774ume]

What does this PR do?

This PR tackles 4 issues:

• Pod Label selection doesn't work OOTB for pods/exec admission selection - this PR implements a check on "admission.datadoghq.com/cws-instrumentation.enabled" manually in the pods/exec admission webhook.
• During a previous refacto, the pods/exec mutating webhook function for "cws-instrumentation" was mistakenly called twice. This PR removes the unnecessary second call.
• Error handling during the remote copy was flaky, this PR improves it to make sure that only successful remote copies return no error.
• By default, cws-instrumentation was copied at the root of the filesystem, but in some cases, the container default user doesn't have write access on /, which is why the default is now to write to /tmp (but it is configurable).

Motivation

This fixes bring us one step closer to enabling this feature by default.

Describe how to test/QA your changes

See #24175

[cit-pr-commenter]

Go Package Import Differences

Baseline: 3945ba0
Comparison: bc749f7

binary	os	arch	change
cluster-agent	linux	amd64	+0, -4 -github.com/mitchellh/go-wordwrap -github.com/moby/term -k8s.io/kubectl/pkg/util/interrupt -k8s.io/kubectl/pkg/util/term
cluster-agent	linux	arm64	+0, -4 -github.com/mitchellh/go-wordwrap -github.com/moby/term -k8s.io/kubectl/pkg/util/interrupt -k8s.io/kubectl/pkg/util/term

[pr-commenter]

Regression Detector

Regression Detector Results

Run ID: 9d8914a3-aaef-4d91-8090-90628fac3bbe Metrics dashboard Target profiles

Baseline: 45fe11b
Comparison: bc79233

Performance changes are noted in the perf column of each table:

• ✅ = significantly better comparison variant performance
• ❌ = significantly worse comparison variant performance
• ➖ = no significant change in performance

No significant changes in experiment optimization goals

Confidence level: 90.00%
Effect size tolerance: |Δ mean %| ≥ 5.00%

There were no significant changes in experiment optimization goals at this confidence level and effect size tolerance.

Fine details of change detection per experiment

perf	experiment	goal	Δ mean %	Δ mean % CI	links
➖	pycheck_1000_100byte_tags	% cpu utilization	+1.36	[-3.50, +6.21]	Logs
➖	otel_to_otel_logs	ingress throughput	+0.05	[-0.76, +0.86]	Logs
➖	uds_dogstatsd_to_api	ingress throughput	-0.00	[-0.00, +0.00]	Logs
➖	tcp_dd_logs_filter_exclude	ingress throughput	-0.00	[-0.01, +0.01]	Logs
➖	file_tree	memory utilization	-0.33	[-0.38, -0.28]	Logs
➖	idle	memory utilization	-0.42	[-0.45, -0.38]	Logs
➖	basic_py_check	% cpu utilization	-0.70	[-3.43, +2.03]	Logs
➖	tcp_syslog_to_blackhole	ingress throughput	-0.97	[-13.46, +11.52]	Logs
➖	uds_dogstatsd_to_api_cpu	% cpu utilization	-2.03	[-2.90, -1.16]	Logs

Explanation

A regression test is an A/B test of target performance in a repeatable rig, where "performance" is measured as "comparison variant minus baseline variant" for an optimization goal (e.g., ingress throughput). Due to intrinsic variability in measuring that goal, we can only estimate its mean value for each experiment; we report uncertainty in that value as a 90.00% confidence interval denoted "Δ mean % CI".

For each experiment, we decide whether a change in performance is a "regression" -- a change worth investigating further -- if all of the following criteria are true:

1. Its estimated |Δ mean %| ≥ 5.00%, indicating the change is big enough to merit a closer look.

2. Its 90.00% confidence interval "Δ mean % CI" does not contain zero, indicating that if our statistical model is accurate, there is at least a 90.00% chance there is a difference in performance between baseline and comparison variants.

3. Its configuration does not mark it "erratic".

[dustmop]

LGTM for agent-shared-components

[pr-commenter]

Test changes on VM

Use this command from test-infra-definitions to manually test this PR changes on a VM:

inv create-vm --pipeline-id=37839186 --os-family=ubuntu

Note: This applies to commit bc749f7

[Gui774ume]

/merge

[dd-devflow]

🚂 MergeQueue: pull request added to the queue

The median merge time in main is 26m.

Use /merge -c to cancel this operation!