Add re-usable Issuable Create app

What does this MR do?

This MR adds a Issuable Create Vue app in FOSS to use in places where want to use Vue to create Issuable. The UX of the form is exact same as HAML view. Please note that the app added in this MR is actually utilized in !41559 (merged) but we're separating it out in this MR.

Screenshots

Desktop	Mobile

Conformity

• 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

#233479 (closed)