Pg15 support

[naisila]

DESCRIPTION: Adds pg15 support

Helpful small PRs to main branch:

• https://github.com/citusdata/citus/pull/6143
• https://github.com/citusdata/citus/pull/6147
• https://github.com/citusdata/citus/pull/6145
• https://github.com/citusdata/citus/pull/6144
• https://github.com/citusdata/citus/pull/6142
• https://github.com/citusdata/citus/pull/6136
• https://github.com/citusdata/citus/pull/6118
• https://github.com/citusdata/citus/pull/6139
• https://github.com/citusdata/citus/pull/6110

[codecov[bot]]

Codecov Report

Merging #6085 (1259d83) into main (1259d83) will not change coverage. The diff coverage is n/a.

:exclamation: Current head 1259d83 differs from pull request most recent head 462d270. Consider uploading reports for the commit 462d270 to get more accurate results

@@           Coverage Diff           @@
##             main    #6085   +/-   ##
=======================================
  Coverage   92.80%   92.80%           
=======================================
  Files         247      247           
  Lines       51996    51996           
=======================================
  Hits        48255    48255           
  Misses       3741     3741           

[naisila]

Note: this PR had earlier done very similar changes to the latest commits in the main branch. I have dropped those commits and force pushed since they were now redundant. For reference:

Commits that were here earlier: https://github.com/citusdata/citus/commit/8faf731168e3e4ebb4cc92c8d3ab3d924956f089 https://github.com/citusdata/citus/commit/8d087f3e637d0a29cf861c6b4f6a490893fa7985 https://github.com/citusdata/citus/commit/397ef6e4e1b6648d9fb5e3093b7a3b26ce0187d4

Commits in main: https://github.com/citusdata/citus/commit/e33ba7da9e750824c9bd8dc3b3c137af3143e99b https://github.com/citusdata/citus/commit/616b1758c2b07154e74a6ae51fddf375f62d0172

[naisila]

HammerDB results with 2 worker nodes, each 16vCPU:

• 52129 NOPM, PG14.5, main branch
• 51161 NOPM, PG15beta3, conn_av_fail branch