Add Webpack, Vue and GitLab UI to Jira Connect app

What does this MR do?

This MR is a subset of changes made in !41285 (closed).

In issue #13020 (closed), we are going to improve how users add namespaces in the Jira Connect app. However, the designs rely heavily on existing UI from GitLab UI. To make our lives easier, it's better to convert the whole thing to Vue. This MR splits out the setup code for Webpack, Vue and GitLab UI for a faster review / merge process.

Screenshots (strongly suggested)

No changes to UI

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry - Not needed since no user facing changes.
• 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