Describe the bug

The "Display timezone" setting is missing UTC.

All my devices and services use UTC to display timestamps.
Correlating logs and events with CheckMate requires to regularly change the
display timezone to one that matches UTC based on the time of year and Daylight Savings Times.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://checkmate-demo.bluewavelabs.ca/settings
2. Click on 'Display timezone'
3. Type in UTC or Etc/UTC or Universal
4. No result is being returned.

Expected behavior
A clear and concise description of what you expected to happen.

Tested against Checkmate 3.1.1 on https://checkmate-demo.bluewavelabs.ca