Auto-embed non-gitlab-managed prometheus alerts

What does this MR do?

This MR adds functionality to the incident issue creation flow. For alerts which come from a manually configured prometheus instance, these changes allow a metrics chart to be embedded in the issue which corresponds to the firing alert.

This depends on a few things to work:

• The project is configured to read prometheus metrics
• The project is configured to receive prometheus alerts
• The alert payload includes some sort of title (under annotations/title or similar)
• The alert payload includes a pointer the the gitlab environment (under labels/gitlab_environment_name)

Issue: #195739 (closed)

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
• 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