Redirecting a request to head TA/lecturer

What does this mr do?

Closes #628

This MR adds the option for TAs to forward requests to all head TAs and lecturers (but not simple TAs) without choosing the specific head TA/lecturer. Then the forwarded request is visible only to [and can only be picked up by] head TAs and lecturers.

The "forwarding enum" would idealy be an actual enum, but I had trouble getting it to work with the database when filtering which requests a person should see.

Screenshots

after

We now have a new option in the forwarding dropdown:

A simple TA does not see that forwarded request:

A teacher does though:

Request indicates that it was forwarded to head TAs/teachers:

Does this MR meet the acceptance criteria?

• I have added a changelog entry to reflect the significant changes I made.
• Tests were created to test the feature.
• I have updated the documentation accordingly.
• I adhere to the style guide.