Improve citus_shard_sizes performance in release-11.3

[halilozanakgul]

This PR combines the relevant parts of #7003, #7018 and the PR that backports those changes to 11.3, #7050 to merge into the 11.3 release branch.

This PR backports the changes to 11.3 release branch, there is another PR, #7062, for 12.0 release branch and one, #7050, for main branch.

[naisila]

It looks like you are doing two backports in a single PR.

772d194
613cced

I think we should do the backports in two separate PRs, each backport pointing to its commit in main in the description. It's also easier to review. After all, the two commits are 1 month apart.

[codecov]

Codecov Report

Merging #7051 (97bebce) into release-11.3 (c18586c) will increase coverage by 18.54%.
The diff coverage is 100.00%.

❗ Current head 97bebce differs from pull request most recent head aca4adb. Consider uploading reports for the commit aca4adb to get more accurate results

@@                Coverage Diff                @@
##           release-11.3    #7051       +/-   ##
=================================================
+ Coverage         74.70%   93.25%   +18.54%     
=================================================
  Files               687      269      -418     
  Lines            131591    57498    -74093     
=================================================
- Hits              98305    53619    -44686     
+ Misses            33286     3879    -29407     

[naisila]

It looks good to me.
Some notes:

• make sure your C changes are identical to the ones in main branch
• would be good to ask another person from the team if it's okay we're backporting two commits in one
• update the description to say that this PR actually backports to 11.3, and the PR to main branch will also include 11.3-2 in the upgrade/downgrade path.

[naisila]

I tested altering the extension locally, both upgrade and downgrade - it worked fine. But we need to add that to our tests.

i.e. We also need to add ALTER EXTENSION tests to multi_extension.sql file, similar to the other lines in that file. Below is an example for 11.2-2--11.3-1

-- Snapshot of state at 11.2-2
ALTER EXTENSION citus UPDATE TO '11.2-2';
SELECT * FROM multi_extension.print_extension_changes();

-- Test downgrade to 11.2-2 from 11.3-1
ALTER EXTENSION citus UPDATE TO '11.3-1';
ALTER EXTENSION citus UPDATE TO '11.2-2';
-- Should be empty result since upgrade+downgrade should be a no-op
SELECT * FROM multi_extension.print_extension_changes();

-- Snapshot of state at 11.3-1
ALTER EXTENSION citus UPDATE TO '11.3-1';
SELECT * FROM multi_extension.print_extension_changes();

[naisila]

Lgtm. Thanks.

Please provide a detailed commit description when you merge.