[8.19] (backport #11219) Allow artifacts.elastic.co URL for manifest downloads

[mergify]

What does this PR do?

This PR adds a new domain from which the packaging process can download manifest artifacts.

Why is it important?

This is part of the effort to reduce the risk of human error when doing an Independent Agent Release version bump in the unified-release repo.

Currently, the version bump is required to find and use the Build ID for the Staging build that was actually released in the previous release.

We are trying to now use part of the new Past Releases API, which now stores the manifest about a past release in a known format. For example: https://artifacts.elastic.co/downloads/9.2.1.json

By using that, we eliminate the manual work needed to find and save the specific Build ID of the Staging build that got promoted to be the actual release.

Currently, the packaging logic does not allow artifacts.elastic.co as a valid domain name form which to download artifacts. This PR fixes that, which will enable the change in the Independent Agent Release.

I mentioned possibly putting this specific domain behind some sort of env var check for whether it was an Independent Agent Release build or not, but @pchila did not think that to be necessary.

Slack convo: https://elastic.slack.com/archives/C054PDS0RCK/p1763139068192439

Related PR: https://github.com/elastic/unified-release/pull/3374

Checklist

• I have read and understood the pull request guidelines of this project.
• My code follows the style guidelines of this project
• 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
• I have added an integration test or an E2E test

Disruptive User Impact

How to test this PR locally

Related issues

Questions to ask yourself

• How are we going to support this in production?
• How are we going to measure its adoption?
• How are we going to debug this?
• What are the metrics I should take care of?
• ...

---

This is an automatic backport of pull request #11219 done by [Mergify](https://mergify.com).

[elasticmachine]

💔 Build Failed

• Buildkite Build
• Commit: 6b076bb

Failed CI Steps

• check-ci
• Unit tests - macOS 15 ARM
• x86_64:sudo: default - platform-ingest-elastic-agent-debian-13-1762801856
• x86_64:sudo: default - platform-ingest-elastic-agent-debian-13-1762801856

History

• 💔 Build #30671 failed 33c6e48

cc @dwhyrock