fix(lib-injection): fix incorrect telemetry data payload format [backport 2.19]

[github-actions]

Backport 7f2e40c from #11950 to 2.19.

We aggregate all telemetry data and then send only once, however we were sometimes aggregating payloads and other times aggregating individual metric events.

This PR fixes the inconsistency by only aggregating the metric events, and sending one single payload at the end.

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-01-17 23:03:16

Comparing candidate commit 6a07e0f in PR branch backport-11950-to-2.19 with baseline commit a08f68a in branch 2.19.

Found 1 performance improvements and 0 performance regressions! Performance is the same for 361 metrics, 2 unstable metrics.

scenario:iast_aspects-ospathjoin_aspect

• 🟩 execution_time [-466.478ns; -398.273ns] or [-8.411%; -7.181%]

[github-actions]

CODEOWNERS have been resolved as:

releasenotes/notes/fix-ssi-telemetry-events-a0a01ad0b6ef63b5.yaml       @DataDog/apm-python
lib-injection/sources/sitecustomize.py                                  @DataDog/apm-core-python