Add observability chains to x-ydb-sdk-build-info

[KirillKurdyukov]

What

• report observability adoption via x-ydb-sdk-build-info
• append tracing/metrics chains in sdk-naming format
• keep chain versions centralized in Observability
• move build-info header population to request metadata path (makeMetadataFromSettings)

Behavior

• observability disabled: header remains unchanged
• existing token ordering/format preserved
• tracing/metrics chain tokens appended only when corresponding client observability is configured

Tests

• DefaultChannelFactoryTest
• YdbDiscoveryTest
• QueryClientBuilderObservabilityTest

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.95%. Comparing base (e77ff50) to head (2b63bd4).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
...ain/java/tech/ydb/table/rpc/grpc/GrpcTableRpc.java	0.00%	4 Missing ⚠️
...ain/java/tech/ydb/core/impl/BaseGrpcTransport.java	75.00%	1 Missing ⚠️
...java/tech/ydb/core/impl/BuildInfoChainSupport.java	66.66%	0 Missing and 1 partial ⚠️
...main/java/tech/ydb/core/impl/auth/GrpcAuthRpc.java	66.66%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #682      +/-   ##
============================================
+ Coverage     71.92%   71.95%   +0.02%     
- Complexity     3466     3477      +11     
============================================
  Files           389      391       +2     
  Lines         16173    16211      +38     
  Branches       1697     1703       +6     
============================================
+ Hits          11633    11665      +32     
+ Misses         3892     3891       -1     
- Partials        648      655       +7     

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