This gives the user the ability to label different account (e.g. "work",
"private") and shows this label in the account switcher. Showing the
label in more places will be done in future MRs.
The label is stored in the user's account data and thus transfers
automatically to other instances of neochat
Fetching the Kirigami Theme via attached properties is expensive. The
theme is also going to be the same for all users so it's enough to only
do it once.
