Stream Rapid Diffs in Merge Requests

What does this MR do and why?

Implements Render a small chunk of MR diffs on the page (#451175 - closed).

This MR changes Rapid Diffs MR view page so it:

1. Renders only first 5 diff files
2. Streams the rest of the diffs with an external request

Screenshots or screen recordings

Screen_Recording_2024-08-15_at_09.06.18

How to set up and validate locally

1. Enable rapid_diffs feature flag
2. Go to any MR with more than 5 files changed
3. Open the 'Changes' tab in a new browser tab
4. Observe the first 5 files rendered with the page, the rest is streamed