Feat: support X-Forwarded-For in gRPC transport

[AkinoKaede]

resolve #1026

[codecov-commenter]

Codecov Report

Merging #1032 (89ff515) into master (8fed55f) will increase coverage by 0.08%.
The diff coverage is 46.66%.

@@            Coverage Diff             @@
##           master    #1032      +/-   ##
==========================================
+ Coverage   44.73%   44.82%   +0.08%     
==========================================
  Files         485      486       +1     
  Lines       29490    29505      +15     
==========================================
+ Hits        13193    13226      +33     
+ Misses      14890    14878      -12     
+ Partials     1407     1401       -6     

Impacted Files	Coverage Δ
transport/internet/grpc/encoding/conn.go	0.00% <0.00%> (ø)
common/protocol/grpc/metadata.go	77.77% <77.77%> (ø)
transport/internet/kcp/connection.go	72.92% <0.00%> (+1.10%)	⬆️
proxy/freedom/freedom.go	49.00% <0.00%> (+4.00%)	⬆️
common/buf/reader.go	88.23% <0.00%> (+5.88%)	⬆️
transport/internet/udp/dispatcher.go	77.14% <0.00%> (+12.38%)	⬆️

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[kslr]

我认为使用最后一个是合理的

[AkinoKaede]

我认为使用最后一个是合理的

是的，不过我觉得应该和 WebSocket 和 HTTP/2 保持一致，或者统一修改。

[github-actions]

It has been open 120 days with no activity. Remove stale label or comment or this will be closed in 5 days

[hann-wang]

LGTM

@xiaokangwang Is there any concern for this PR?