feat: Add session closed metric

[KirillKurdyukov]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 82.85714% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.19%. Comparing base (ae5b7db) to head (0fbd104).
⚠️ Report is 10 commits behind head on master.

Files with missing lines	Patch %	Lines
...java/tech/ydb/table/impl/pool/StatefulSession.java	41.66%	2 Missing and 5 partials ⚠️
...src/main/java/tech/ydb/query/impl/SessionPool.java	90.00%	0 Missing and 3 partials ⚠️
...ain/java/tech/ydb/table/impl/pool/SessionPool.java	85.71%	0 Missing and 1 partial ⚠️
...in/java/tech/ydb/table/impl/pool/WaitingQueue.java	93.33%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #700      +/-   ##
============================================
+ Coverage     71.88%   72.19%   +0.31%     
- Complexity     3475     3500      +25     
============================================
  Files           390      391       +1     
  Lines         16206    16315     +109     
  Branches       1698     1707       +9     
============================================
+ Hits          11649    11779     +130     
+ Misses         3906     3883      -23     
- Partials        651      653       +2     

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