Make report_issues.vue easily extendable

What does this MR do?

Establish the ground structure to properly implement two Deliverable :

• https://gitlab.com/gitlab-org/gitlab-ce/issues/45318
• https://gitlab.com/gitlab-org/gitlab-ee/issues/5488 while still providing a better maintainability and easier extensibility in the FE code.

See the very relevant EE-Portion of this MR:

• https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/6667

Does this MR meet the acceptance criteria?

• [n.a] Changelog entry added, if necessary
• [n.a] Documentation created/updated
• [n.a] API support added
• [n.a] Tests added for this feature/bug
• Conforms to the code review guidelines
  • Has been reviewed by a Frontend maintainer
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #49614 (closed)