fix: default cors plugin formdata validation error

[liuxiran]

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

Why submit this pull request?

• Bugfix
• New feature provided
• Improve performance
• Backport patches

What changes will this PR take into?

when I submitted default cors plugin configure in form mode, a validation error occured:

the error shows that allow_origins_by_regex should have at least 1 character.

• Reason

schema of cors plugin:

{
    "properties": {
        ...
	"allow_origins_by_regex": {
	    "description": "you can use regex to allow specific origins when no credentials,for example use [.*\\.test.com] to allow a.test.com and b.test.com",
	    "items": {
		 "maxLength": 4096,
		 "minLength": 1,
		 "type": "string"
	    },
	    "minItems": 1,
	    "type": "array",
	    "uniqueItems": true
	},
    },
   "type": "object"
}

shows that allow_origins_by_regex is not a required item, but when it configured, it should be at least 1 character.

the default post data is:

{
    "allow_credential": false
    "allow_headers": "*"
    "allow_methods": ["*"]
    "allow_origins": "*"
    "allow_origins_by_regex": [""]
    "expose_headers": "*"
    "max_age": 5
}

the mistake is "allow_origins_by_regex": [""], why the value is [""]? In order to make UI better to use, we set default allow_origins_by_regex empty to have one input box in the page.

• How to fix
  omit allow_origins_by_regex when it is not configured

Checklist:

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

[netlify]

Deploy preview for apisix-dashboard ready!

Built with commit 07b9a7c

https://deploy-preview-1855--apisix-dashboard.netlify.app

[codecov-commenter]

Codecov Report

Merging #1855 (bf445c8) into master (b1e66a2) will increase coverage by 0.36%.
The diff coverage is 100.00%.

❗ Current head bf445c8 differs from pull request most recent head 07b9a7c. Consider uploading reports for the commit 07b9a7c to get more accurate results

@@            Coverage Diff             @@
##           master    #1855      +/-   ##
==========================================
+ Coverage   72.10%   72.47%   +0.36%     
==========================================
  Files         125      125              
  Lines        2947     2950       +3     
  Branches      711      712       +1     
==========================================
+ Hits         2125     2138      +13     
+ Misses        822      812      -10     

Flag	Coverage Δ
frontend-e2e-test	72.47% <100.00%> (+0.36%)	⬆️

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

Impacted Files	Coverage Δ
web/src/components/Plugin/UI/cors.tsx	86.95% <ø> (+21.73%)	⬆️
web/src/components/Plugin/PluginDetail.tsx	65.75% <100.00%> (+2.81%)	⬆️
web/src/helpers.tsx	72.13% <0.00%> (+3.27%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b1e66a2...07b9a7c. Read the comment docs.

[imjoey]

/lgtm
Thanks.