fix: Remove unnecessary serde_json dependency from logs feature and ensure opentelemetry-proto compatibility

[Copilot]

The logs feature in opentelemetry-sdk/Cargo.toml was unnecessarily including serde_json as a dependency. After thorough analysis of the codebase, I confirmed that:

• No logs-related code in src/logs/ uses serde_json
• The serde_json dependency is correctly included in the jaeger_remote_sampler feature where it's actually needed for JSON parsing in the Jaeger remote sampler implementation
• The logs feature works perfectly without this dependency

However, removing serde_json from the logs feature caused build failures in opentelemetry-proto when the with-serde feature was enabled, as it relied on the transitive dependency from the SDK. To resolve this:

Changes made:

1. opentelemetry-sdk/Cargo.toml: Removed serde_json from the logs feature

   # Before
   logs = ["opentelemetry/logs", "serde_json"]
   
   # After  
   logs = ["opentelemetry/logs"]

2. opentelemetry-proto/Cargo.toml: Added serde_json as an optional dependency when with-serde is enabled

   # Before
   with-serde = ["serde", "const-hex", "base64"]
   
   # After
   with-serde = ["serde", "const-hex", "base64", "serde_json"]

This change reduces unnecessary dependencies for users who only need logging functionality without the Jaeger remote sampler feature, while ensuring that opentelemetry-proto has access to serde_json when JSON serialization/deserialization is needed.

Fixes #3104.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.5%. Comparing base (e0dd566) to head (bead802).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #3114   +/-   ##
=====================================
  Coverage   80.5%   80.5%           
=====================================
  Files        126     126           
  Lines      22218   22218           
=====================================
+ Hits       17889   17890    +1     
+ Misses      4329    4328    -1     

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[cijothomas]

@copilot the build fails as opentelemetry-proto relied on serde_json from the sdk/logs! Modify opentelemetry-proto to bring serde_json if with-serde feature is enabled in the opentelemetry-proto

[Copilot]

@copilot the build fails as opentelemetry-proto relied on serde_json from the sdk/logs! Modify opentelemetry-proto to bring serde_json if with-serde feature is enabled in the opentelemetry-proto

I've fixed the build issue by adding serde_json as an optional dependency to opentelemetry-proto when the with-serde feature is enabled. The changes ensure that the build no longer fails when opentelemetry-proto requires serde_json for JSON serialization/deserialization tests and functionality. Build verified with various feature combinations. (commit bead802)