Support downloading universal and pure Python wheels

[trishankatdatadog]

What does this PR do?

New downloader for new Agents that will download and verify both universal and pure Python wheels.

Motivation

Request to support both types of wheels.

Additional Notes

This only affects new Agents. Old downloaders in old Agents will continue to work.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• PR must have changelog/ and integration/ labels attached

[trishankatdatadog]

Right now, the integration test running the downloader on every integration will fail, saying something like:

tuf.exceptions.UnknownTargetError: u'in-toto-metadata/2.root.layout' not found.

This is because the repository has not been updated with this new root layout yet. We should be doing that early next week.

[codecov]

Codecov Report

Merging #4981 into master will decrease coverage by 1.23%.
The diff coverage is n/a.

Impacted Files	Coverage Δ
datadog_checks_base/tests/conftest.py	33.33% <0%> (-66.67%)	⬇️
...atadog_checks_base/datadog_checks/base/__init__.py	73.33% <0%> (-13.34%)	⬇️
datadog_checks_base/tests/test_winpdh.py	90.9% <0%> (-6.82%)	⬇️
datadog_checks_base/datadog_checks/base/ddyaml.py	56.71% <0%> (-4.48%)	⬇️
datadog_checks_base/tests/test_http.py	94.39% <0%> (-4.01%)	⬇️
datadog_checks_base/tests/test_pdhbasecheck.py	96% <0%> (-4%)	⬇️
clickhouse/datadog_checks/clickhouse/clickhouse.py
vertica/tests/metrics.py
fluentd/tests/test_metadata.py
rabbitmq/tests/test_rabbitmq.py
... and 304 more

[ofek]

🥇

[ofek]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 2 pipeline(s).

[trishankatdatadog]

OK, we look good to go 🚀

Just to clarify, this is for datadog-agent>=6.16.0.

Also, could we please bump the datadog-checks-downloader from 0.6.0 to 2.0.0? This is to make it sparkling clear that this version of the downloader is explicitly tied to v2 of our software supply chain (2.root.layout), which requires supplying the Python tag when verifying a wheel.