Fixed text on how to get the functions' final URL

What does this MR do?

Until now the docs said to get the function's URL from the job logs. This is much less friendly than getting the URL from the Serverless page, moreover, since a tm tool upgrade, the job logs don't even contain the URL. As we want to support the URL on the UI, not in the job log, the docs was adjusted accordingly.

Screenshots

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 #196567 (closed)