Use GlAlert for errors in Jira Connect app

What does this MR do?

Towards #13019 (closed)

This MR displays a GlAlert component when an error occurs in the Jira Connect App. The browser alert has been removed in this MR.

Iteration	MR
Move jira_connect JS to Vue App	!48744 (merged)
Add basic shared state to Jira Connect Vue app	!48750 (merged)
Improve shared state	!51046 (merged)
Render gitlab-ui alert on error	👉 You are here

Screenshots (strongly suggested)

Demo video

Video	Screenshot
demo

Below screenshots to show that the sign-in page is not affected

Before	After

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 #13019 (closed)