Use streamed diffs on commits page

What does this MR do and why?

This MR changes Rapid Diffs commit view page so it:

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

Similar to the work done in !160695 (merged).

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

stream_4_files

How to set up and validate locally

1. Enable rapid_diffs feature flag
2. Go to any commit with more than 5 files changed
3. Add ?rapid_diffs=true&view=parallel to the URL.
4. Observe the first 5 files rendered with the page, the rest is streamed

Related to #451177