Read pull_request and pull_request_target event info from GHA

[juan-fernandez]

What and why?

GitHub does not run workflows in the head of the branch about to be merged whenever the workflow is triggered through pull_request or pull_request_target events. It runs them in a merge commit. This is the one that we add to git.commit.sha. This is sometimes confusing because this commit does not exist in the history of the branch. What we did:

• Notice when this happens
• When it does, add a new set of tags:
  • git.commit.head_sha, which is the head SHA of the feature branch (branch to be merged).
  • git.pull_request.base_branch_sha, which is the head SHA of the base branch (branch you're merging into)
  • git.pull_request.base_branch, which is the name of the base branch

How?

Detect if we're in a pull_request or pull_request_target event by checking GITHUB_BASE_REF, and if we are, attempt to read the event.json payload made available by GitHub in GITHUB_EVENT_PATH.

Review checklist

• Feature or bugfix MUST have appropriate tests (unit, integration)

[datadog-datadog-prod-us1]

Datadog Report

Branch report: juan-fernandez/add-extra-tags-pull-request
Commit report: e98ab98
Test service: datadog-ci-tests

✅ 0 Failed, 8424 Passed, 0 Skipped, 3m 53.76s Total Time

[Drarig29]

The changed helpers look good to me (from Synthetics CT)