Drops PG14 support

[naisila]

DESCRIPTION: Drops PG14 support

1. Remove "$version_num" != 'xx' from configure file
2. delete all PG_VERSION_NUM = PG_VERSION_XX references in the code
3. Look at pg_version_compat.h file, remove all _compat functions etc defined specifically for PGXX differences
4. delete all PG_VERSION_NUM >= PG_VERSION_(XX+1), PG_VERSION_NUM < PG_VERSION_(XX+1) ifs in the codebase
5. delete ruleutils_xx.c file
6. cleanup normalize.sed file from pg14 specific lines
7. delete all alternative output files for that particular PG version, server_version_ge variable helps here

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.44%. Comparing base (c55bc8c) to head (9b510e6).
Report is 6 commits behind head on release-13.0.

Additional details and impacted files

@@               Coverage Diff                @@
##           release-13.0    #7753      +/-   ##
================================================
- Coverage         89.48%   89.44%   -0.04%     
================================================
  Files               276      276              
  Lines             60063    59897     -166     
  Branches           7524     7510      -14     
================================================
- Hits              53747    53576     -171     
- Misses             4166     4176      +10     
+ Partials           2150     2145       -5     

[onurctirtir]

Code & test output changes look good to me. Will do another pass once the branch is rebased & polished and the conflicts are resolved.