Add Configuration for SMPP provider character encoding

[abdulazizali77]

/kind feature

What happened: An SMS Provider character encoding is determined by the provider itself. When incoming message DCS==0 the message character encoding may be a GSM7, or ASCII

What you expected to happen: For DCS==0 we need to look up the configured provider's character encoding so we may encode the outgoing message correctly

How to reproduce it (as minimally and precisely as possible):

Anything else we need to know?:

Environment: 8.3.0-190