Make manual prom configs always editable

What does this MR do?

Contributres to #207233 (closed).

This MR keeps the manual Prometheus configuration section always editable. Previously, if auto-configuration was enabled, the manual configs section was hidden. This MR makes it so the user can have both auto/manual editable. However, the manual configs will always take precedence, which has always been the case.

Find the configurations sections here Manual Configuration > Project-level auto-configuration > Group-level > Instance-level

Screenshots

Note that

1. Manual configuration is always editable
2. A sentence is added under the manual configuration section title. (The last screenshot has the updated text)

--	--
Before - this will change
After (without existing auto-config)
After (with existing auto-config)
After (with manual configs enabled) - remains the same as before
With text change

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
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

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