Implement pagination in the file tree browser

What does this MR do and why?

Currently, the File tree browser only loads page 1 of the paginated list for each directory.. This MR displays a Show more button when a directory contains more than 1 page (more than 100 items). When the button is clicked, the next page will be fetched.

⚠️ Note: fetching nested items if the user is currently viewing a nested item that is not on page 1 will be handled in a follow-up.

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Enable the repository_file_tree_browser feature flag
2. Navigate a repository/directory containing many files
   • Feel free to clone this project if you need many files
3. A show more button should render below lists containing more than 100 items
4. Clicking Show more should fetch the next page

MR acceptance checklist

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Related to #550196 (closed)