feat(appsec): enable telemetry when appsec is enabled through the tracer and not the extension

[florentinl]

What does this PR do?

This PR does the two following things:

• Enable instrumentation telemetry when DD_APPSEC_ENABLED=true, the same way the extension wrapper script does when DD_SERVERLESS_APPSEC_ENABLED:
  https://github.com/DataDog/datadog-lambda-extension/blob/main/scripts/datadog_wrapper#L38

• Prevent pruning of *.dist-info/METADATA files in the layer. These files are required for Appsec Software Composition Analysis to extract the Name and Version of dependencies:
  https://github.com/DataDog/dd-trace-py/blob/main/ddtrace/internal/packages.py#L25-L43

Motivation

In the continuity of moving from the extension implementation of appsec for python to the tracer, having functional runtime Software Composition Analysis is part of the scope.

Testing Guidelines

Manual testing for now, and system-tests will be coming soon.

Because the feature is entirely implemented on the dd-trace-py side, I don't think it makes a lot of sense to add unit tests here.

Additional Notes

I reused the env variable instead of relying on the config module. Importing the config module resulted in cyclic imports that caused a lot of tests to fail for reasons I don't fully understand. I have not investigated further.

Types of Changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog
• This PR passes the integration tests (ask a Datadog member to run the tests)