fix: do not pre-bind for BindXXX interface & normalize content-type

[FGYFFFF]

What type of PR is this?

fix

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• [x] This PR title match the format: \<type>(optional scope): \<description>
• [x] The description of this PR title is user-oriented and clear enough for others to understand.
• [x] Attach the PR updating the user documentation if the current PR requires user awareness at the usage level. User docs repo

(Optional) Translate the PR title into Chinese.

使用BindXXX()接口时，无需做提前的 pre-bind；并且对 content-type 做归一化处理

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

en: do not pre-bind for BindXXX interface & normalize content-type zh(optional): 使用BindXXX()接口时，无需做提前的 pre-bind；并且对 content-type 做归一化处理

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[codecov[bot]]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (0619701) 82.52% compared to head (9a6d2f2) 82.54%.

Files	Patch %	Lines
pkg/app/context.go	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #1060 +/- ## =========================================== + Coverage 82.52% 82.54% +0.02% =========================================== Files 98 98 Lines 10025 10026 +1 =========================================== + Hits 8273 8276 +3 + Misses 1255 1254 -1 + Partials 497 496 -1 ```

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