feat(io): add info metric to pushgateway writer

[AndreyMarkinPPC]

• Ignore unset columns
• Process built-in virtual columns

[codecov-commenter]

Codecov Report

❌ Patch coverage is 84.61538% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.67%. Comparing base (5ebb9d2) to head (b50ad7a).
⚠️ Report is 284 commits behind head on main.

Files with missing lines	Patch %	Lines
libs/io/garf/io/writers/pushgateway_writer.py	60.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #483      +/-   ##
==========================================
+ Coverage   88.23%   90.67%   +2.44%     
==========================================
  Files          61       85      +24     
  Lines        2600     4570    +1970     
==========================================
+ Hits         2294     4144    +1850     
- Misses        306      426     +120     

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