Create 25.10 release branch and configure CI/CD for weekly backports

[niedbalski]

We need to create the release/25.10 branch to serve as the stable branch for the October 2025 release series.
The plan is to:

• Branch off from the current main (based on 4.0.x series).
• Keep backporting relevant fixes and improvements from 4.0.x to release/25.10.
• Configure CI/CD to handle weekly releases from this branch.
• Maintain main as the base for the next major series (post-4.0.x).

Tasks:

• Create the release/25.10 branch.
• Update CI pipelines to support weekly releases from this branch.
• Ensure backport process from 4.0.x is documented.
• Validate all unit/integration tests pass on the branch.
• Announce branch creation and release plan in Slack.

Notes:

• Keep parity with 4.0.x bug fixes where relevant.
• Do not block the branch creation on BATS test improvements (tracked separately).