Improve the SMS notification sending mechanism

[janakamarasena]

Is your suggestion related to an experience ? Please describe. Internally Identity Server handles sending SMS notifications in two ways. While SMS otp has its own way of sending SMSs, places such as self-registration with SMS verification and mobile number update verification depend on carbon-analytics streams based notification sending.

Describe the improvement The mechanisms of sending notification should be unified and the new method used in sms otp should be used in other places.

Additional context Having DB based publisher configs has a issue when loading them as well as mentioned in https://github.com/wso2/product-is/issues/19471#issuecomment-1953850218