Apply user timezone to date headers in commits list

What does this MR do and why?

Contributes to #417311 (closed)

Problem

We use a system timezone for date headers in commits list page. It leads to situations when users see a date from past or future if they use a custom non-UTC timezone.

Solution

Apply user timezone to date headers.

Screenshots or screen recordings

http://127.0.0.1:3000/gitlab-org/gitlab-test/-/commits/master

Before (date header without timezone applied)	After (with timezone from user's profile)

My timezone is UTC+2.

MR acceptance checklist

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