Translate function URL if cluster has serverless domain

What does this MR do?

Solves #38336 (closed)

Important! this MR should not be merged before the ServerlessDomain.generate method is created, therefore it has WIP prefix, although the requirements of the #38336 (closed) are met, as per @ali-gitlab comment on the issue.

The changes from MR implementing Gitlab::Serverless::Domain Gitlab::Serverless::FunctionURI are part of this MR now. Only when that MR is merged, it's safe to merge this one.

This MR generates a translated function URL if the cluster has serverless domain and returns this new URL to the frontend. The translation will be done in ServerlessDomain.generate, in this MR it's stubbed by function FunctionsController#generate_url.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #38336 (closed)