Add GlAlert with link to Jira issue

What does this MR do?

Changes:

• Add external-icon next to author name since the link will open to a remote location.
• Add missing statusIcon prop for issue status which is only shown on mobile.
• Add a GlAlert with some information mentioning this is a Jira issue with a link to the original issue.
• Update link from Jira issue list page to point to this new Jira issue details page (instead of opening the original issue in Jira).

Relevant issue: #298724 (closed)

🇦🇨 These changes are behind the feature flag jira_issues_show_integration

Progress

MR	Status
Render empty Jira issue in GitLab (behind feature flag)	✅ Done
Add Jira issues show mock endpoint and add basic frontend structure	✅ Done
Add sidebar to individual Jira issues show	🚧 WIP
Add custom breadcrumb for Jira issues show	🚧 WIP
Add GlAlert with link to Jira issues show	👈 You are here
Add error handling to Jira issues show	🚧 WIP
More MRs to come	...

Screenshots (strongly suggested)

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