transport: add metrics when it s active

[hugehoo]

Fixes: #8529
RELEASE NOTES: N/A

This PR fixes to increment metrics only when the stream is active which is found in the activeStreams map.

as-is

• The deleteStream was incrementing channelz metrics every time it was called, even when stream was already removed from activeStreams or not exists in activeStreams.

to-be

• Added check to ensure metrics are only incremented once when a stream is actually removed from activeStreams.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.67%. Comparing base (8420f3f) to head (e856376).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8573      +/-   ##
==========================================
- Coverage   80.91%   80.67%   -0.24%     
==========================================
  Files         413      413              
  Lines       40751    40771      +20     
==========================================
- Hits        32972    32893      -79     
- Misses       6155     6220      +65     
- Partials     1624     1658      +34     

Files with missing lines	Coverage Δ
internal/transport/http2_server.go	87.40% <100.00%> (-3.48%)	⬇️

... and 19 files with indirect coverage changes

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