Users: allow email format to be configured

Allowing the email format to be configure would make the system more generic.

Edit:
We can start by supporting some static formats

- F-sektionen TLTH
- F-tek Chalmers

And then we can build out the list and allow configuration from ENV?

Start by locating where user email formats are assembled and where environment configuration is read. Review the requested F-sektionen TLTH and F-tek Chalmers formats, then define what configuration and supported-format behavior the issue should cover. Done means the requested formats can be selected without changing application code, with coverage for the supported choices.

Written by the indexing model from the issue text.