fix: (route_online_debug)Change the appended Content-type data to overlay to ensure that the Content-type is unique

[Jaycean]

Please answer these questions before submitting a pull request

• Why submit this pull request?

• Bugfix

• New feature provided

• Improve performance

• Backport patches

• Related issues

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Bugfix

• Description
  There is a bug in the use process. The user writes the Content-type to the header-params to forward the content type of the URL. The old logic uses the req.Header.Add method to generate multiple Content-type values, which leads to the failure of the forwarding request.

• How to fix?
  use req.Header.Set To override the ·Content-type· and ensure that the value is unique。

[liuxiran]

related fe pr: #1612

[codecov-io]

Codecov Report

Merging #1619 (d84ab27) into master (f4f27d1) will decrease coverage by 9.84%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1619      +/-   ##
==========================================
- Coverage   71.77%   61.93%   -9.85%     
==========================================
  Files         133       47      -86     
  Lines        5471     3118    -2353     
  Branches      592        0     -592     
==========================================
- Hits         3927     1931    -1996     
+ Misses       1301      874     -427     
- Partials      243      313      +70     

Flag	Coverage Δ
backend-e2e-test	61.93% <100.00%> (-0.03%)	⬇️
backend-e2e-test-ginkgo	48.07% <100.00%> (-0.02%)	⬇️
backend-unit-test	?
frontend-e2e-test	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...l/handler/route_online_debug/route_online_debug.go	75.92% <100.00%> (+1.41%)	⬆️
api/internal/utils/runtime/runtime.go	0.00% <0.00%> (-64.29%)	⬇️
api/internal/core/store/validate_mock.go	0.00% <0.00%> (-50.00%)	⬇️
api/internal/core/store/store.go	58.43% <0.00%> (-30.73%)	⬇️
api/internal/filter/authentication.go	47.22% <0.00%> (-30.56%)	⬇️
api/internal/handler/service/service.go	62.60% <0.00%> (-29.57%)	⬇️
api/internal/filter/ip_filter.go	48.71% <0.00%> (-23.08%)	⬇️
api/internal/handler/global_rule/global_rule.go	64.51% <0.00%> (-19.36%)	⬇️
...pi/internal/handler/plugin_config/plugin_config.go	59.57% <0.00%> (-18.09%)	⬇️
api/internal/utils/json_patch.go	44.82% <0.00%> (-13.80%)	⬇️
... and 99 more

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[nic-chen]

LGTM

[Jaycean]

cc @liuxiran @LiteSun @juzhiyuan FE CI Failed PTAL. Thks.

[liuxiran]

mark fe e2e errors:

• search route error: https://github.com/apache/apisix-dashboard/pull/1619/checks?check_run_id=2146696140
• create-edit-delete consumer error: https://github.com/apache/apisix-dashboard/pull/1619/checks?check_run_id=2150934899

fixed by two test commits

[liuxiran]

fe local test passed, LGTM