Add Jira Import form

What does this MR do?

This MR adds the Jira Import form. There is no logic associated with the form and is purely UI. The logic will be added in this follow-up MR: !29128 (merged)

To view it, activate the feature flags below and visit http://localhost:3000/gitlab-org/gitlab-test/-/import/jira (you need to make sure Jira integration has been activated for the project, otherwise you will see a Set up Jira integration screen)

Feature flags: :jira_issue_import and :jira_issue_import_vue

Issue: #208907 (closed)

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