Update timezone format (UTC and number)

Proposal:

Update TimezoneDropdown timezone formatting done in date_format_utility.js#419, there are current extra white space which makes annoying to read and not visually pleasant. Current UTC - 11, UTC + 11

Mind that the helper used there affects multiple places multiple places (at the time of writing /profile, group/project/-/pipeline_schedules/ and Settings -> CI/CD -> Deploy freeze)

Updated format should be:

For -	For +	For 0
No space, ex UTC-11	No space, ex UTC+11	1 space between, ex UTC 0

Visual differences between before and now

Current	New

Context: review of the TimezoneDropdown migration !101384 (comment 1141022884)