[9.0](backport #4895) bk: use GCP OIDC

[mergify]

What is the problem this PR solves?

Remove static service accounts and the security concerns around it.

How does this PR solve the problem?

• Use GCP OIDC to copy the logs to the private storage.
• Use gcloud instead of gsutil (so it honours the Env variables)
• Tear-down is now managed by the BK plugin itself.

How to test this PR locally

In the CI:

• https://buildkite.com/elastic/fleet-server-package-mbp/builds/1929
• https://buildkite.com/elastic/fleet-server/builds/8230#0196aa44-0505-475c-a325-da00a219be3f

Produced

2025-05-07 13:49:22 UTC | If you have a compatible Python interpreter installed, you can use it by setting
  | 2025-05-07 13:49:22 UTC | the CLOUDSDK_PYTHON environment variable to point to it.
  | 2025-05-07 13:49:22 UTC |  
  | 2025-05-07 13:49:26 UTC | Copying file://build/distributions/fleet-server-fips-9.1.0-SNAPSHOT-linux-arm64.tar.gz.sha512 to gs://fleet-server-ci-internal/jobs/commits/29b03ada4cc6bc8b735d8d616c662818aa84eb3e/fleet-server-fips-9.1.0-SNAPSHOT-linux-arm64.tar.gz.sha512
  | 2025-05-07 13:49:26 UTC | Copying file://build/distributions/fleet-server-fips-9.1.0-SNAPSHOT-linux-arm64.tar.gz to gs://fleet-server-ci-internal/jobs/commits/29b03ada4cc6bc8b735d8d616c662818aa84eb3e/fleet-server-fips-9.1.0-SNAPSHOT-linux-arm64.tar.gz
  | 2025-05-07 13:49:27 UTC | Completed files 2/2 \| 7.5MiB/7.5MiB
  | 2025-05-07 13:49:28 UTC |  

Design Checklist

• I have ensured my design is stateless and will work when multiple fleet-server instances are behind a load balancer.
• I have or intend to scale test my changes, ensuring it will work reliably with 100K+ agents connected.
• I have included fail safe mechanisms to limit the load on fleet-server: rate limiting, circuit breakers, caching, load shedding, etc.

Checklist

• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool

Related issues

---

This is an automatic backport of pull request #4895 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of d4d19b2 has failed:

On branch mergify/bp/9.0/pr-4895
Your branch is up to date with 'origin/9.0'.

You are currently cherry-picking commit d4d19b2.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   .buildkite/pipeline.yml
	modified:   .buildkite/scripts/common.sh
	modified:   .buildkite/scripts/dra_release.sh
	modified:   .buildkite/scripts/package.sh
	modified:   .buildkite/scripts/release_test.sh

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   .buildkite/hooks/pre-command
	both modified:   .buildkite/hooks/pre-exit
	both modified:   .buildkite/pipeline.package.mbp.yml

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[prodsecmachine]

🎉 Snyk checks have passed. No issues have been found so far.

✅ security/snyk check is complete. No issues have been found. (View Details)

✅ license/snyk check is complete. No issues have been found. (View Details)

[v1v]

Requires #4934

[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