Resolve "Access project from descendent groups when selecting project to create new issue"

What does this MR do?

• Expose the existing only_owned and include_subgroups of GroupProjectsFinder to the Groups API

• Update project selection dropdowns to hide shared projects and include projects in subgroups. This is to make it consistent with the projects of the issues / MRs listed in the page.

  This applies to:

  • Group Issues Page - New Issue for Project Dropdown
  • Group Merge Requests Page - New Merge Request for Project Dropdown
  • Group Boards > New Issue > Project Selector

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.

Closes #52453 (closed) Closes #47096 (closed)