`--engine` Flag Ignored in `apppack create database` Command

[CuriousLearner]

It appears that the --engine flag in the apppack create database command is being ignored, requiring users to manually select from a dropdown.

If the flags are provided, the questions shouldn't be asked again.

[ipmb]

Same goes for --cluster

[CuriousLearner]

I have changed this, however I think the problem is that without the --engine flag, it defaults to postgres. I've also defaulted to non-aurora instance. Is this okay, or we need something else here? We can document this, but I'm still indecesive and would appreciate a second set of eyes on this.