feat: support trailer

[byene0923]

What type of PR is this?

feat

Check the PR title.

• This PR title match the format: <type>(optional scope): <description>
• The description of this PR title is user-oriented and clear enough for others to understand.

(Optional) Translate the PR title into Chinese.

增加 HTTP Trailer 支持

(Optional) More detail description for this PR(en: English/zh: Chinese).

en:

• add Trailer struct to RequestHeader and ResponseHeader
• implement trailer read and write for http1.1

zh(optional):

• 为RequestHeader 和 ResponseHeader 增加 Trailer 结构
• 为 http1.1 实现 trailer 的读和写

Which issue(s) this PR fixes:

#201

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Base: 71.43% // Head: 72.12% // Increases project coverage by +0.69% 🎉

Coverage data is based on head (04a431c) compared to base (773cd67).
Patch coverage: 76.58% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #474      +/-   ##
===========================================
+ Coverage    71.43%   72.12%   +0.69%     
===========================================
  Files           93       94       +1     
  Lines         9000     9234     +234     
===========================================
+ Hits          6429     6660     +231     
+ Misses        2181     2155      -26     
- Partials       390      419      +29     

Impacted Files	Coverage Δ
pkg/protocol/http1/ext/stream.go	0.00% <0.00%> (ø)
pkg/protocol/http1/req/header.go	65.44% <40.00%> (-0.98%)	⬇️
pkg/protocol/request.go	83.85% <50.00%> (-0.44%)	⬇️
pkg/protocol/http1/ext/common.go	21.13% <54.38%> (+11.65%)	⬆️
pkg/protocol/http1/resp/response.go	70.67% <76.92%> (+0.51%)	⬆️
pkg/protocol/header.go	77.05% <78.12%> (+0.49%)	⬆️
pkg/protocol/http1/req/request.go	62.20% <81.81%> (+0.31%)	⬆️
pkg/protocol/trailer.go	89.38% <89.38%> (ø)
pkg/protocol/args.go	82.62% <100.00%> (+0.76%)	⬆️
pkg/protocol/http1/resp/header.go	79.36% <100.00%> (+0.50%)	⬆️
... and 4 more

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[welkeyever]

reviewer + @byene0923 🙏