feat: CRDs ingressClassName field cannot be modified

[AlinsRan]

Type of change:

• Bugfix
• New feature provided
• Improve performance
• Backport patches
• Documentation
• Refactor
• Chore
• CI/CD or Tests

What this PR does / why we need it:

Ref: #1719

Pre-submission 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

[codecov-commenter]

Codecov Report

Merging #1728 (0a48f58) into master (38710e7) will decrease coverage by 0.38%.
The diff coverage is 11.17%.

❗ Current head 0a48f58 differs from pull request most recent head d900ee9. Consider uploading reports for the commit d900ee9 to get more accurate results

@@            Coverage Diff             @@
##           master    #1728      +/-   ##
==========================================
- Coverage   39.72%   39.35%   -0.38%     
==========================================
  Files          92       91       -1     
  Lines        8065     8063       -2     
==========================================
- Hits         3204     3173      -31     
- Misses       4457     4484      +27     
- Partials      404      406       +2     

Impacted Files	Coverage Δ
pkg/api/server.go	50.00% <0.00%> (-32.72%)	⬇️
pkg/api/validation/apisix_plugin_config.go	0.00% <0.00%> (ø)
pkg/api/validation/apisix_route.go	0.00% <0.00%> (-24.60%)	⬇️
pkg/api/validation/validator.go	0.00% <0.00%> (ø)
...kg/providers/apisix/translation/apisix_upstream.go	60.75% <0.00%> (-1.58%)	⬇️
pkg/api/validation/utils.go	45.28% <80.00%> (+12.85%)	⬆️
cmd/ingress/ingress.go	83.33% <100.00%> (+0.14%)	⬆️
pkg/api/router/webhook.go	100.00% <100.00%> (ø)
pkg/config/config.go	64.64% <100.00%> (+0.36%)	⬆️

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