It seems replicationfactor and writeconcern fields cannot be set. At least they are not documented.
type: database
action: create
name: attach
allowed:
- username: ${user}
password: ${password}
replicationfactor: 3 <-- seems missing
writeconcern: 2 <-- seems missing

It seems
replicationfactorandwriteconcernfields cannot be set. At least they are not documented.