Conditionally render policy alert editor

What does this MR do?

Conditionally render policy alert editor

• check if any agents have been installed and configured
• show the policy alert picker if an agent has been added, do now show it if no agent has been added
• create help urls to guide the user
• Abstract out policy editor data to helper

Screenshots (strongly suggested)

Before	After with agent	After without agent	After with alert but without agent

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

Related to #297463 (closed)