Add validation for short username

[kshitijrajsharma]

There's no error per se about single character names. The API will still search for the stats associated with that name.

• This should be also blocked from api end as well , osm allows min 3 character to have username as per this discussion cc: @ramyaragupathy

Originally posted by @kshitijrajsharma in https://github.com/hotosm/galaxy-ui/issues/112#issuecomment-1176112468