Add option for explicit keystore/truststore password for mountedDir

[HoustonPutman]

Resolves #603

The Cert Manager CSI Driver only accepts a string password when creating pkcs12 keystores, so we need to support this.

This will be tested by #605 , which isn't great, but any issues will be fixed there.

TODO:

• [x] Changelog entry
• [x] Helm Chart
• [x] Documentation