OIDC Enhancements

[kumo-rn5s]

What this PR does:

• Adds support for custom claim keys for roles, usernames, and avatar URLs in OIDC configuration.
• Enables the use of custom authorization, token, and user info endpoints.
• Allows the OIDC client to retrieve additional user information from the UserInfo endpoint.
• Adds an example for the Okta provider.

Why we need it:

• Provides greater flexibility in configuring OIDC providers, especially when the default claim keys or endpoints do not match the user's setup.
• Ensures the OIDC client can retrieve more user information from the UserInfo endpoint.
• Enhances compatibility with various OIDC providers.

Which issue(s) this PR fixes:
Fixes #5330

Does this PR introduce a user-facing change?:
Yes

• How are users affected by this change:

  • Users can now specify custom claim keys for roles, usernames, and avatar URLs in their OIDC configuration. They can also set custom endpoints for authorization, token, and user info.
  • The UserInfo endpoint will be automatically used to get additional claim fields.
  • Users can now specify custom userinfo/authorize/token endpoints on the prerequisites of issuer discovery.

• Is this a breaking change:
  No

• How to migrate (if breaking change):
  Not applicable

[t-kikuc]

Thank you! Let me check for some weeks