If User Does not set admin username then create a username with random string

[kgcarr]

for security, we should not have a default admin user named admin

[chenzhiwei]

just get a chance to review the code, I think the operator should expose the secret name that contains the username and password.

The approach should be something like:

spec:
  mongoCredentialRef: mongo-user

In the controller logic:

1. The default value of mongoCredentialRef should be mongo-user.
2. If user want to customize the user/pass, they can create a secret before installing

   kubectl create secret generic mongo-user --from-literal username=user --from-literal password=pass
   

3. If this secret does not exist, then the controller should create one with random values

[kgcarr]

I think this is a good recommendation. It will have to be Q2 at this point though