Use paginated tree query for retrieving repository files

What does this MR do?

Uses the new paginated Tree GraphQL query to display files in the repository browser.

Screenshots or Screencasts (strongly suggested)

No visual changes are expected apart from the query loading returning the correct amount of files:

FF disabled	FF enabled

How to setup and validate locally (strongly suggested)

This feature is behind the :paginated_tree_graphql_query feature flag.

1. run rails c in the project root
2. run Feature.enable(:paginated_tree_graphql_query) in the rails console
3. view a repository with files

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Related to #334140 (closed)