fix(openapi): enable ReDoc when Swagger UI is disabled

[4lxndr]

Q	A
Branch?	4.2
Tickets	#7608
License	MIT
Doc PR	-

Fixes the issue where ReDoc cannot be used as the sole documentation UI. When enable_swagger_ui was false and enable_re_doc was true, accessing /api/docs.html resulted in a 404 "Swagger UI is disabled" error.

Changes:

• Load swagger_ui services when either Swagger UI or ReDoc is enabled
• Add reDocEnabled parameter to DocumentationAction
• Use SwaggerUiProcessor for both Swagger UI and ReDoc rendering
• Update service definitions to pass enable_re_doc parameter

This allows ReDoc to work independently when Swagger UI is disabled, while maintaining backward compatibility when both are enabled.

Fixes #7608

[4lxndr]

CI was fine and went partially red after squash. Retry?

Feedback welcome.

[soyuka]

thanks!