Fetch more group projects

What does this MR do?

Related to #250684 (closed)

The GraphQL API only returns a max of 100 projects at a time. This sets up an observer to watch for when the user scrolls to the bottom of the dropdown, and fetches the next "page" of projects.

Screenshots

Scrolling to the bottom loads more

fetch_more_projects_scroll

Searching for a project that hasn't been loaded yet loads more

fetch_more_projects_search

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