[cmd/mdatagen] Fix Histogram metric generation logic & reduce zapgrpc noise

[EdgeN8v]

Fixes #14326
Fixes #5169

Description:
This PR contains fixes for two separate issues (committed on the same branch):

1. [cmd/mdatagen]: Fixes a bug where the Record function for Histogram metrics was generated with missing parameters (sum, bucketCounts).
2. [zapgrpc]: Filters out noisy "http2Server.HandleStreams failed to read frame" warnings which occur when clients disconnect.

Testing:

• I have added a Histogram metric (system.cpu.utilization) to samplescraper metadata to verify that the generated code compiles correctly.

[codecov]

Codecov Report

❌ Patch coverage is 78.00000% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.10%. Comparing base (bf28fa7) to head (4119f04).
⚠️ Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
otelcol/internal/grpclog/logger.go	15.38%	11 Missing ⚠️

❌ Your patch check has failed because the patch coverage (78.00%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14327      +/-   ##
==========================================
- Coverage   92.14%   92.10%   -0.04%     
==========================================
  Files         668      668              
  Lines       41529    41578      +49     
==========================================
+ Hits        38266    38296      +30     
- Misses       2228     2244      +16     
- Partials     1035     1038       +3     

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