Rules for usernames / logonnames

[fforootd]

As an administrator I want to be able to define a username convention so if we do have multiple administrators we all set the same usernames.

• I can set rules how a username should look like
• I can set which characters should not be included (e.g. emojies)

Additional Context

Discussed in #3956

^{Originally posted by yasukawa426 July 13, 2022}
Right now you are able to write anything you want in your username, for example, you can use whitespace or even emojis. It would be a good idea to be able to create rules to username just like you can with the passwords.

[fforootd]

relates to #4344

[fforootd]

CC @hifabienne

[hifabienne]

We will change the suffix/domain verification to optin on the username #4245
With this change it will be possible to use emails as username and this might need some rules (e.g domain)
As soon as we can set some rules, we can get rid of the suffix part completaly.

We might consider actions for the rules, where we just provide some specific templates for email validation, etc. Its difficult to predict what kind of rules we need in the future, with the action we are flexible in this part.

[fforootd]

We should also consider if a user is allowed to change its username with this ruleset

Asked here https://discord.com/channels/927474939156643850/1025633876804116540/1025633876804116540

[hifabienne]

I think this is also a topic for the #6433