Add links section in metrics dashboard

What does this MR do?

Users can define custom links in the dashboard yml file that are generated as anchor tags on the metrics dashboard.

Links format in yml file

links:
  - title: GitLab Website
    url: https://gitlab.com
  - title: https://docs.gitlab.com
    url: GitLab docs

Sample dashboard files for testing

links_without_titles.yml

links_with_long_titles.yml

links_without_urls.yml

few_links.yml

many_links.yml

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

Mentions #216385 (closed)