[Elastic-Agent] Allow to specify what artifacts to embed at build times

[ph]

We need to embed signatures files at build times to allow us to verify the artifacts in the work in #19222. The Elastic Agent is built by the release manager which also builds all the other artifacts.

We need to change the order of operation.

• build filebeat/create signature.
• build metricbeat/create signature file
• build endpoint/create signature file.
• build Elastic-Agent with the right "archives" and the right signature files.

To do this we could have at parameters at build times to specify what needs to be embedded.

[elasticmachine]

Pinging @elastic/ingest-management (Team:Ingest Management)

[Conky5]

To be clear the order of operations today looks like:

1. All beats projects are built
2. release-manager generates signature files
3. downstream codesigning jobs are run
4. release-manager re-generates signature files for codesigned artifacts

What I think we'll want it to look like:

1. All beats projects minus elastic-agent are built
2. release-manager generates signature files
3. downstream codesigning jobs are run
4. release-manager re-generates signature files for codesigned artifacts
5. The elastic-agent build runs, which is passed the fully signed artifacts and signature files by release-manager, which are then bundled into the elastic-agent distribution
6. release-manager generates signature files for the elastic-agent archives

[michalpristas]

this one's already in place, closing