Use timezones for Danger Reviewer Roulette implementation

What does this MR do?

This prioritize choosing a reviewers/maintainers for which the current time is between 6AM and 2PM (this is so that someone that starts in approx. 2 hours, or finish in approx. 4 hours can be chosen).

The goal is to try out this new strategy for a 1-month duration before choosing if we want to keep it or not: https://gitlab.com/gitlab-org/quality/team-tasks/-/issues/563. Feedback is welcome at #227123 (closed).

Also, has_capacity is now already factored in available (see https://gitlab.com/gitlab-org/gitlab-roulette/-/blob/a8751be15554dc3adc7d9139febcdef7d4433be4/lib/team_member.rb#L49).

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Separation of EE specific content

Todos before merging

• Communicate broadly about this change:
  • Slack
  • Eng. Week in Review

Closes #216875 (closed).