Add a property to enable the disk encryption for postgres databases on AWS

[max-soe]

We added the possibility to use encrypted disks for AWS Postgres Databases. The new property can be used during the inital deployment. Changes for already existing databases are not supported. Terraform would replace them with complete data lose.

Implementation steps:

- Add a KMS Key + Alias and connect them to the database
- Add a cli property to use the encrypted disk for AWS
- Deploy KMS Key + Alias only if the disk encryption is enabled
- Update the documentation

[SaphMB]

Thanks for the contribution @max-soe!