feat(grpc): add grpc metadata api

[HeyJavaBean]

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[codecov[bot]]

Codecov Report

Base: 61.88% // Head: 61.67% // Decreases project coverage by -0.20% :warning:

Coverage data is based on head (9443e12) compared to base (b758335). Patch coverage: 17.28% of modified lines in pull request are covered.

:exclamation: Current head 9443e12 differs from pull request most recent head 3093843. Consider uploading reports for the commit 3093843 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #672      +/-   ##
===========================================
- Coverage    61.88%   61.67%   -0.21%     
===========================================
  Files          214      214              
  Lines        16647    16489     -158     
===========================================
- Hits         10302    10170     -132     
+ Misses        5361     5346      -15     
+ Partials       984      973      -11     

Impacted Files	Coverage Δ
client/stream.go	59.18% <0.00%> (-15.18%)	:arrow_down:
pkg/remote/trans/nphttp2/stream.go	57.77% <0.00%> (-42.23%)	:arrow_down:
pkg/remote/trans/nphttp2/meta_api.go	7.89% <7.89%> (ø)
pkg/remote/trans/nphttp2/grpc/http2_client.go	71.67% <60.00%> (+0.69%)	:arrow_up:
pkg/remote/trans/nphttp2/peer/peer.go	85.71% <85.71%> (ø)
pkg/remote/trans/nphttp2/client_handler.go	54.28% <100.00%> (+1.34%)	:arrow_up:
pkg/remote/trans/nphttp2/server_handler.go	65.15% <100.00%> (+0.26%)	:arrow_up:
internal/wpool/pool.go	87.09% <0.00%> (-2.10%)	:arrow_down:
pkg/remote/trans/nphttp2/grpc/transport.go	59.80% <0.00%> (-1.92%)	:arrow_down:
pkg/gofunc/go.go	87.50% <0.00%> (-1.39%)	:arrow_down:
... and 10 more

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