Allow users to change their handle

[DragonSenseiGuy]

We should allow users to change their handles with a timeout of ~7 days if noone had that handle for >=14 days. We will probably need to keep a log of handle changes, and this will involve a Prisma migration!

[DragonSenseiGuy]

This should be easy enough to implement, can I get this @ascpixi ?

[ascpixi]

Of course, thank you so much! <3