Add baggage support

[siri-varma]

Description

Please explain the changes you've made

Issue reference

We strive to have all PR being opened based on an issue, where the problem or feature have been discussed prior to implementation.

Please reference the issue this PR will close: #[issue number]

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Extended the documentation

[siri-varma]

@artur-ciocanu / @cicoyle / @javier-aliaga / @salaboy Please take a look at this PR when you get a chance. Thanks

[javier-aliaga]

@siri-varma I ask copilot to review, lets see what it suggest, I will do my own review tomorrow

[Copilot]

Pull request overview

Adds W3C baggage propagation support to the Dapr Java SDK so that baggage can flow through both gRPC and HTTP calls via Reactor context, and includes a new example + gRPC-focused tests.

Changes:

• Add Headers.BAGGAGE constant and propagate it through HTTP header allowlist.
• Introduce DaprBaggageInterceptor and wire it into the gRPC interceptor chain.
• Add a baggage example and a new gRPC unit test suite validating propagation behavior.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
sdk/src/test/java/io/dapr/client/DaprClientGrpcBaggageTest.java	New gRPC tests validating baggage propagation behavior.
sdk/src/main/java/io/dapr/internal/grpc/interceptors/DaprBaggageInterceptor.java	New gRPC client interceptor injecting baggage into metadata from Reactor context.
sdk/src/main/java/io/dapr/internal/grpc/DaprClientGrpcInterceptors.java	Wires the new baggage interceptor into the existing interceptor chain.
sdk/src/main/java/io/dapr/client/Headers.java	Adds a public BAGGAGE header constant.
sdk/src/main/java/io/dapr/client/DaprHttp.java	Allows baggage to be promoted from Reactor context into outgoing HTTP headers.
examples/src/main/java/io/dapr/examples/baggage/README.md	New documentation for the baggage example.
examples/src/main/java/io/dapr/examples/baggage/BaggageClient.java	New runnable example demonstrating baggage propagation via Reactor context.

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[siri-varma]

@copilot can you fix the comments ?

[codecov]

Codecov Report

❌ Patch coverage is 86.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.54%. Comparing base (f63a4a4) to head (fe166be).

Files with missing lines	Patch %	Lines
...rnal/grpc/interceptors/DaprBaggageInterceptor.java	84.61%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1659      +/-   ##
============================================
+ Coverage     79.53%   79.54%   +0.01%     
- Complexity     2193     2196       +3     
============================================
  Files           237      238       +1     
  Lines          6577     6591      +14     
  Branches        730      732       +2     
============================================
+ Hits           5231     5243      +12     
  Misses          990      990              
- Partials        356      358       +2     

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[siri-varma]

@javier-aliaga Addressed all the comments. Thank you.