Gradually load more diffs as time goes on

What does this MR do?

To increase the loading performance of diffs with this we are increasing the number of diffs per page, starting off with a small number to quickly show diffs and then load more per page after that.

This changes for single diff file mode - if the user has this enabled we will load 1 diff file first so we can get a diff on the screen quickly. After this has loaded, we fall back to gradually increase page size as time goes on.

Screenshots (strongly suggested)

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

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #224161 (closed)