feat: add support for password grant in keycloak plugin and in dashboard

[azilentech]

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

Why submit this pull request?
This PR is in the context of PR of API SIX, apache/apisix#6586

Support of password grant type for token generation in keycloak plugin.

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

What changes will this PR take into?

Please update this section with a detailed description.

Related issues

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 #2376 (bf9b3a8) into master (561ed37) will decrease coverage by 19.90%.
The diff coverage is 27.88%.

❗ Current head bf9b3a8 differs from pull request most recent head e763063. Consider uploading reports for the commit e763063 to get more accurate results

@@             Coverage Diff             @@
##           master    #2376       +/-   ##
===========================================
- Coverage   68.52%   48.62%   -19.91%     
===========================================
  Files         131       42       -89     
  Lines        3419     3270      -149     
  Branches      826        0      -826     
===========================================
- Hits         2343     1590      -753     
- Misses       1076     1476      +400     
- Partials        0      204      +204     

Flag	Coverage Δ
backend-unit-test	48.62% <27.88%> (?)
frontend-e2e-test	?

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

Impacted Files	Coverage Δ
api/internal/core/entity/entity.go	0.00% <ø> (ø)
api/internal/core/store/storehub.go	0.00% <0.00%> (ø)
api/internal/filter/cors.go	0.00% <0.00%> (ø)
api/internal/handler/data_loader/route_export.go	70.74% <0.00%> (ø)
api/internal/handler/data_loader/route_import.go	26.68% <0.00%> (ø)
api/internal/utils/utils.go	49.07% <0.00%> (ø)
...pi/internal/handler/system_config/system_config.go	58.00% <58.00%> (ø)
web/src/pages/Consumer/Create.tsx
web/src/pages/Consumer/List.tsx
web/src/pages/Consumer/components/Step1.tsx
... and 169 more

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