uis mutations: log the user

[oliver-sanders]

For scheduler commands, we always log the user who actioned the command (unless they are workflow owner, in which case it is implicit).

However, there are some things that are implemented at the UIS not the scheduler e.g:

• The play mutation.
• The log query (although this is a mutation, it causes cylc cat-log commands to be run).

We should log the user who actioned these operations.

E.G. add the user name here:

https://github.com/cylc/cylc-uiserver/blob/f6a05fc5212d7f3bdbd6d525f5660135fa198f75/cylc/uiserver/resolvers.py#L300

Make this match the format we use in the scheduler.