Mechanism for encrypting ssl_key

The ssl_key setting is used to defined the private key used for SSL/TLS connections.

We need the ability to obfuscate the contents of that file, e.g. as a PKCS#12 keystore like some of the clients support. Request is to add a mechanism for specifying a keystore password in the configuration.
Ideally, this will have the option to use a file or a value; as with "file_key_management_filekey=FILE:" in the file_key_management plugin.