[DOP-20061] Stats for relations response

[TiGrib]

Change Summary

Add stats for Output and Input relations.
num_bytes, num_files, num_rows.

Related issue number

[DOP-20061]

Checklist

• Commit message and PR title is comprehensive
• Keep the change as small as possible
• Unit and integration tests for the changes exist
• Tests pass on CI and coverage does not decrease
• Documentation reflects the changes where applicable
• docs/changelog/next_release/<pull request or issue id>.<change type>.rst file added describing change
  (see CONTRIBUTING.rst for details.)
• My PR is ready to review.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.36%. Comparing base (6d4ffe3) to head (e1aea76).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #105      +/-   ##
===========================================
+ Coverage    92.30%   92.36%   +0.06%     
===========================================
  Files          154      154              
  Lines         3341     3355      +14     
  Branches       227      227              
===========================================
+ Hits          3084     3099      +15     
+ Misses         200      199       -1     
  Partials        57       57              

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