Add application create API

Original MR by @PNSalocin: gitlab-org/gitlab-ce!8160

What does this MR do?

Adding an API for creating applications.

Why was this MR needed?

It resolves https://gitlab.com/gitlab-org/gitlab-ce/issues/24035

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • [-] Has been reviewed by UX
  • [-] Has been reviewed by Frontend
  • Has been reviewed by Backend
  • [-] Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered

What are the relevant issue numbers?

Closes #24035 (closed)