CI: Add branch matrix to support testing on main and REL_2_STABLE

[tuhaihe]

Currently, the CI pipeline only targets the Cloudberry main branch. This commit enhances the workflow to support multi-branch testing by introducing a matrix strategy.

Key changes:

• Add cloudberry_branch matrix to build-cloudberry-deb and pxf-test jobs to run parallel workflows for main and REL_2_STABLE.
• Include the sanitized branch name in the DEB package version (e.g., 99.0.0-REL-2-STABLE) to differentiate artifacts.
• Update artifact upload/download paths to prevent collision between Or branches.
• Improve the test summary script to group and report results by Cloudberry branch.

closes: #ISSUE_Number

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[leborchuk]

LGTM, see running tests for both main and REL_2_STABLE branches.

I also see that we have listed protected (by launching tests) branches in section cloudberry_branch.

It's easy to forget to add the REL_3_STABLE branch when it appears. May we document it somewhere in main repo? For example, create document, what not to forget to do when creating a new stable branch. I also going to add support testing workflow for various cloudberry branches to other projects like yezzey. It would be great if we had a unified approach.

[tuhaihe]

We can hold on to merge this PR. Maybe we can have a new branch REL_2_STABLE for the PXF release.