Add away toggle for TAs

[ribhavsharma]

Description

Adds back an away toggle for TAs per queue.

Closes #171

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• This requires a run of yarn install
• This change requires an addition/change to the production .env variables. These changes are below:
• This change requires developers to add new .env variables. The file and variables needed are below:
• This change requires a database query to update old data on production. This query is below

Checklist:

• I have performed a code review of my own code (under the "Files Changed" tab on github) to ensure nothing is committed that shouldn't be (e.g. leftover console.logs, leftover unused logic, or anything else that was accidentally committed)
• I have commented my code where needed
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have checked that new and existing tests pass locally with my changes
• Any work that this PR is dependent on has been merged into the main branch
• Any UI changes have been checked to work on desktop, tablet, and mobile

Screenshot

[AdamFipke]

See comments. Big things are:

• Tests
• Mobile
• Showing "Away" for Queue Invites page

Overall though, I think this is a pretty minimal implementation which I like.

I also made a follow up issue that you might be interested in if you have time #430

[AdamFipke]

Changes look good!

I also thought having the "Away" switch by the "Staff" header looked so good on mobile that I moved it there on desktop too.

before

after

Also the "Away" status on queue invite page looks to be working!