Add changelog for 12.1.7

[eaydingol]

Add changelog entries for 12.1.7

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.60%. Comparing base (cb31a64) to head (ac75b77).
Report is 7 commits behind head on release-12.1.

Additional details and impacted files

@@               Coverage Diff                @@
##           release-12.1    #7889      +/-   ##
================================================
+ Coverage         89.57%   89.60%   +0.02%     
================================================
  Files               276      276              
  Lines             59660    59661       +1     
  Branches           7448     7448              
================================================
+ Hits              53442    53459      +17     
+ Misses             4081     4063      -18     
- Partials           2137     2139       +2     

[onurctirtir]

https://github.com/citusdata/citus/actions/runs/13175327676/job/36773269693?pr=7889

Seems check-style on this branch failed with this error message:

We allow at most 80 characters in CHANGELOG.md.
( 113 characters ) : * Avoids re-assigning the global pid for client backends and bg workers when the application_name changes (#7791)
( 89 characters ) : * Raises an ERROR instead of server crash for certain scenarios, e.g, Bug 3697586 (#7836)
( 106 characters ) : * Fixes tests: foreign_key_to_reference_shard_rebalance test ...

After the updating the entries, we can shorten the long ones as in here, if we still have any;

* foo foo foo foo foo foo foo ...
  foo foo foo foo foo foo foo ...
  foo foo foo ..

[onurctirtir]

The other CI jobs are failing just because they're flaky.

We can re-run them and they will probably pass.

Other option that I usually prefer is to do a github search for the test name in this repo to see if we merged a commit into another branch, probably main, to make that test not flaky, and then to cherry-pick it to the release branch so that next time we don't have the same issue. If you prefer to do that, cherry-picking them in this PR is fine as long as we don't squash the commits when merging the PR.

[onurctirtir]

Let's squash merge this PR.

And although soon we'll re-create main branch from release-13.0 (as an exception for this release), our convention is still to cherry-pick the changelog updates to main too. Once you open a PR for that, I can quickly approve it.

And there is one more thing that needs to be done in another PR for release branch before creating 12.1.7 tag - we need to bump the version to 12.1.7 as in 15ecc37.

[hanefi]

I agree with Onur as we need to squash these changes into a single commit.