Better conversion of AtExceptions to @ protocol error codes

[gkc]

Describe the bug

• Some valid AtExceptions are not mentioned in the error_codes conversion map in at_commons/lib/src/exception/error_message.dart
• When one of those AtExceptions is thrown, it results in error responses to clients like this error:null-null : ...

Expected behaviour

• All AtExceptions need to be included in the error_codes conversion map
• Consider also extending at_commons error_message.dart with a way to create (not throw, just create) the correct exception given an error code. (We currently have mapping from exception to error-code but not the other way around). This makes it easier for servers to intelligently 'forward' exceptions (for example as described in https://github.com/atsign-foundation/at_server/issues/509)

[gkc]

@kalluriramkumar As per our discussion. If you want to pick this one up, please assign yourself and go ahead!

[gkc]

@kalluriramkumar Is this obsolete now?

[XavierChanth]

@gkc @sitaram-kalluri can this be closed?