EPIC: Add a Post-Build job and Sign-SBOM job

[andrew-m-leonard]

Create a new job "Post-Build" which implements issue, this encompasses all post-build tasks. To this job we will then run a new job "Sign-SBOM" on the "signing node", with the available RSA key.

• Compiles and build TemurinSignSBOM
• Signs and Verifies SBOM Signature

Publishes Artifacts:

• Signed SBOM artifact

Tasks:

• [x] #1105
• [ ] Request Adoptium PEM private&public key pair from EF, request
• [ ] https://github.com/adoptium/temurin-build/issues/3946
• [ ] Create new Post-Build job, and a new Sign-SBOM job using TemurinSignSBOM

[smlambert]

Additional post build tasks to consider hanging off of this job:

• Triggering release notes job
• Auto-creation of draft PR for next release blog post (to use to capture 'featured' items ahead of time)

[smlambert]

Additional Post-build task

• EclipseMirror activity (currently a job on TC Jenkins) to backup release tarballs (job runs on TC Jenkins server, but potentially can be remotely triggered from this Post-build job to consolidate triggering of various tasks in one spot)

[sxa]

Also download testing as per https://github.com/adoptium/temurin-build/issues/3506 which includes SBoM validation.

This is currently performed by the standalone download_and_sbom_validation job which uses the release_download_test.sh script