Format sources

[artemgavrilov]

This PR adds Makefile targets that format sources according to PG rules and CI workflow that checks that opened pull request has formatted sources (CI fails if sources are not formatted).

https://wiki.postgresql.org/wiki/Running_pgindent_on_non-core_code_or_development_code
https://github.com/postgres/postgres/blob/master/src/tools/pgindent/README

[codecov]

Codecov Report

Attention: Patch coverage is 95.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 84.87%. Comparing base (1aa3081) to head (d5b73bc).
Report is 1 commits behind head on main.

Files	Patch %	Lines
pg_stat_monitor.c	91.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #475      +/-   ##
==========================================
- Coverage   84.98%   84.87%   -0.11%     
==========================================
  Files           3        3              
  Lines        1292     1296       +4     
  Branches      197      198       +1     
==========================================
+ Hits         1098     1100       +2     
  Misses         98       98              
- Partials       96       98       +2     

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[darkfronza]

LGTM