Show date when relative time is over a year old

What does this MR do and why?

This prevents confusing relative times since a year is a long period and a relative time like "a year ago" could mean 1 year and 1 day or 1 year and 364 days.

References

Related to #18607 (closed)

Screenshots or screen recordings

Issue list and other places should show the date instead of the relative time:

Repository list should not be affected:

How to set up and validate locally

1. Enable the show_date_when_relative_time_over_a_year feature flag
2. Check anywhere we render relative times. These should show as dates when over a year except for the repository file list.

MR acceptance checklist

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