feat: Proxy the related requests to apisix

[monkeyDluffy6017]

Please answer these questions before submitting a pull request, or your PR will get closed.

Why submit this pull request?

• [ ] Bugfix
• [x] New feature provided
• [ ] Improve performance
• [ ] Backport patches

What changes will this PR take into?

The backend of apisix-dashboard currently has many of the same interfaces as apisix, and there are differences in implementation, resulting in inconsistent between apisix and apisix-dashboard, and every change to the apisix interface will result in changes to apisix-dashboard. This is a lot of work. The apisix-dashboard backend has now been modified to only proxy related requests to apisix, and is no longer implemented separately.

Checklist:

• [x] Did you explain what problem does this PR solve? Or what new features have been added?
• [x] Have you added corresponding test cases?
• [x] Have you modified the corresponding document?
• [ ] Is this PR backward compatible? If it is not backward compatible, please discuss on the mailing list first

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[codecov-commenter]

Codecov Report

Merging #2634 (857c66d) into next (005ed14) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##             next    #2634   +/-   ##
=======================================
  Coverage   41.72%   41.72%           
=======================================
  Files          15       15           
  Lines         405      405           
=======================================
  Hits          169      169           
  Misses        213      213           
  Partials       23       23           

Flag	Coverage Δ
backend-unit-test	41.72% <ø> (ø)

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[monkeyDluffy6017]

And, why have many CIs been removed?

@bzp2010 I just want to test backend-e2e-test-v3, i will add the deleted ci files later