feat: add proto binder for GRPCProxyWrapper

[sysulq]

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[codecov-commenter]

Codecov Report

Merging #652 (bf72130) into master (5e4b020) will decrease coverage by 0.31%.
The diff coverage is 25.09%.

@@            Coverage Diff             @@
##           master     #652      +/-   ##
==========================================
- Coverage   53.06%   52.75%   -0.32%     
==========================================
  Files         190      191       +1     
  Lines       10114    10381     +267     
==========================================
+ Hits         5367     5476     +109     
- Misses       4348     4482     +134     
- Partials      399      423      +24     

Impacted Files	Coverage Δ
pkg/server/xecho/error.go	0.00% <ø> (ø)
pkg/server/xecho/status.go	36.73% <ø> (ø)
proto/testproto/v1/hello.pb.go	38.81% <0.00%> (-1.33%)	⬇️
test/e2e/server/xgrpcgateway.go	100.00% <ø> (ø)
pkg/server/xecho/bind.go	21.79% <21.79%> (ø)
pkg/server/xecho/handler.go	39.13% <42.30%> (+39.13%)	⬆️
pkg/core/tests/http.go	89.74% <100.00%> (+0.26%)	⬆️
test/e2e/server/xecho.go	100.00% <100.00%> (ø)
pkg/registry/etcdv3/registry.go	72.26% <0.00%> (+1.02%)	⬆️
... and 4 more

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