Remove the minimum username length restriction

[hhhguany]

Is your enhancement request related to a problem? Please describe

I use OAuth to connect accounts. Many users have 3-character usernames in the existing external account system, so is it possible to remove the minimum username length restriction.

Describe the solution you'd like

Remove the minimum username length restriction.

Describe alternatives you've considered

Set the minimum username length to 2.

[zahash]

i'll do this

[zahash]

here is the PR

#1127