Enable nightly minor version builds

[claytonparnell]

Issue #, if available:

Description of changes:

Add a new workflow which runs on the 1st-10th of each month, triggering minor version build every day. Reads support_policy.md to determine active Major versions, then checks build_artifacts/v* to determine the latest minor/patch version per major version. Calls build-image for minor version, using latest patch of each major version as base.

Also update build-image to allow for repeated calls for same version, with two main changes:

1. If branch already exists, merge main into it. If not, create new branch.
2. If PR already exists, fetch the PR ID for calling CodeBuild. If not, create new PR.

Ran locally using act, got output matrix={"version":["1.13.1","2.5.0","3.0.0"]} as expected:

[Kickoff nightly Minor version builds/Generate version matrix] ⭐ Run Set up job
[Kickoff nightly Minor version builds/Generate version matrix] 🚀  Start image=catthehacker/ubuntu:act-latest
[Kickoff nightly Minor version builds/Generate version matrix]   🐳  docker pull image=catthehacker/ubuntu:act-latest platform= username= forcePull=true
[Kickoff nightly Minor version builds/Generate version matrix]   🐳  docker create image=catthehacker/ubuntu:act-latest platform= entrypoint=["tail" "-f" "/dev/null"] cmd=[] network="host"
[Kickoff nightly Minor version builds/Generate version matrix]   🐳  docker run image=catthehacker/ubuntu:act-latest platform= entrypoint=["tail" "-f" "/dev/null"] cmd=[] network="host"
[Kickoff nightly Minor version builds/Generate version matrix]   🐳  docker exec cmd=[node --no-warnings -e console.log(process.execPath)] user= workdir=
[Kickoff nightly Minor version builds/Generate version matrix]   ✅  Success - Set up job
[Kickoff nightly Minor version builds/Generate version matrix] ⭐ Run Main actions/checkout@v4
[Kickoff nightly Minor version builds/Generate version matrix]   🐳  docker cp src=/local/home/crpjr/sagemaker-distribution/. dst=/local/home/crpjr/sagemaker-distribution
[Kickoff nightly Minor version builds/Generate version matrix]   ✅  Success - Main actions/checkout@v4 [1.359867649s]
[Kickoff nightly Minor version builds/Generate version matrix] ⭐ Run Main echo run_name
[Kickoff nightly Minor version builds/Generate version matrix]   🐳  docker exec cmd=[bash -e /var/run/act/workflow/1] user= workdir=
[Kickoff nightly Minor version builds/Generate version matrix] Kickoff Minor nightly builds 04-23-2025
[Kickoff nightly Minor version builds/Generate version matrix]   ✅  Success - Main echo run_name [116.85246ms]
[Kickoff nightly Minor version builds/Generate version matrix] ⭐ Run Main Get supported Major versions
[Kickoff nightly Minor version builds/Generate version matrix]   🐳  docker exec cmd=[bash -e /var/run/act/workflow/supported-major-versions] user= workdir=
[Kickoff nightly Minor version builds/Generate version matrix]   ✅  Success - Main Get supported Major versions [119.38658ms]
[Kickoff nightly Minor version builds/Generate version matrix]   ⚙  ::set-output:: majors=["1","2","3"]
[Kickoff nightly Minor version builds/Generate version matrix] ⭐ Run Main Generate base patch version matrix
[Kickoff nightly Minor version builds/Generate version matrix]   🐳  docker exec cmd=[bash -e /var/run/act/workflow/gen-mat] user= workdir=
[Kickoff nightly Minor version builds/Generate version matrix]   ✅  Success - Main Generate base patch version matrix [129.458025ms]
[Kickoff nightly Minor version builds/Generate version matrix]   ⚙  ::set-output:: matrix={"version":["1.13.1","2.5.0","3.0.0"]}
[Kickoff nightly Minor version builds/Generate version matrix] ⭐ Run Complete job
[Kickoff nightly Minor version builds/Generate version matrix] Cleaning up container for job Generate version matrix
[Kickoff nightly Minor version builds/Generate version matrix]   ✅  Success - Complete job

Patch versions will need more discussion for the cadence we want to use

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