Username index is incorrectly setup

[krtk6160]

@dolcalmi had mentioned that our username index is setup incorrectly. I ran .explain() in mongosh on some of the queries that use username to lookup users, and found that they indeed do not make use of the username index.

@dolcalmi How should this be fixed?

[dolcalmi]

I think we should use Case Insensitive Index but also we need to update username query (without regex)

[nicolasburtey]

could we get case insensitive username with proper index still? that's a useful feature to set the case when you set up a username. I know it makes indexing a lot more complex.

[dolcalmi]

fixed