Support importing CA certificates into custom truststore

[leochr]

CA certificates are imported into the default generated truststore. Add the same support to custom truststore that users may want to bring. They could specify the truststore location and password using TRUSTSTORE_FILE and TRUSTSTORE_PASSWORD env variables.

[leochr]

@arturdzm if you have some cycles in December, this would be something good to investigate/think about. The default truststore scenarios should be looked at again I think. Thank you.