Move jira_connect.js code to Vue App

What does this MR do?

Towards #13019 (closed)

Iteration	MR
Move jira_connect JS to Vue App	👉 You are here
Add basic shared state to Jira Connect Vue app	!48750 (merged)
Render gitlab-ui alert on error	!48651 (merged)

This MR consolidates all Javascript for the Jira Connect app to 1 file. Previously, we had 2 files.

Why?

• Performance - 1 file is better than 2
• To support #13019 (closed). Consolidating the legacy jquery code and the Vue code means we can use a shared state (!48750 (merged)). This won't be forever - we will iterate away from jquery and eventually this entire form will be in Vue.

Screenshots (strongly suggested)

No visual changes

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