Add test collector plugin for Buildkite analytics

[rowlandgeoff]

Add the test collector plugin to enable Buildkite test analytics. Test results will be shown here after main branch pipeline runs: https://buildkite.com/organizations/elastic/analytics/suites/fleet-server

Closes https://github.com/elastic/ingest-dev/issues/3916

[mergify]

This pull request does not have a backport label. Could you fix it @rowlandgeoff? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-./d./d is the label to automatically backport to the 8./d branch. /d is the digit

[mergify]

backport-8.x has been added to help with the transition to the new branch 8.x.
If you don't need it please use backport-skip label and remove the backport-8.x label.

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarQube

[alexsapran]

I have no comment; we did in other repositories, but IMHO, it's not ideal either—except Beats, due to the nature of the pipelines.

The secret should be in a repository-scoped vault path rather than a shared vault path. This is a good idea because the secret makes sense only for this repository.

[rowlandgeoff]

Do we have repo-scoped vault paths that we use for CI?

[alexsapran]

sure we do https://docs.elastic.dev/ci/using-secrets#using-repository-scoped-secrets

But we can move them afterwards.

[jlind23]

Looks good to me, were you able to have a successful run on your PR already?

[rowlandgeoff]

Looks good to me, were you able to have a successful run on your PR already?

@jlind23 Yes, had 2 successful runs on the PR before I switched it to only run on main.

[jlind23]

@rowlandgeoff Let's merge it then :-)