docs: add comment for method Redirect and Header

[Tom-debug110]

What type of PR is this?

docs: Documentation only changes

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补充 RequestContext 的Redirect 和Header 方法的注释,以 Gin 中对应的方法注释为模版,降低理解成本

(Optional) Which issue(s) this PR fixes:

#867

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[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (c0512ff) 81.82% compared to head (ca6f05a) 81.85%.
Report is 3 commits behind head on develop.

❗ Current head ca6f05a differs from pull request most recent head 2f739b5. Consider uploading reports for the commit 2f739b5 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #868      +/-   ##
===========================================
+ Coverage    81.82%   81.85%   +0.03%     
===========================================
  Files           98       98              
  Lines         9926     9926              
===========================================
+ Hits          8122     8125       +3     
+ Misses        1314     1311       -3     
  Partials       490      490              

Files	Coverage Δ
pkg/app/context.go	93.41% <ø> (ø)

... and 1 file with indirect coverage changes

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[welkeyever]

LGTM, thx~