generate a per service base exception

[aajtodd]

Currently we generate something like:

SdkBaseException < ServiceException < com.example.foo.SomeException

OR in case of AWS services

SdkBaseException < ServiceException < AwsServiceException < aws.sdk.kotlin.foo.SomeException

We should consider changing this to generate a per/service base exception such that the hierarchy looks like:

SdkBaseException < ServiceException < com.example.foo.SomeException < com.example.foo.SomeException

// AWS equivalent

SdkBaseException < ServiceException < AwsServiceException < aws.sdk.kotlin.foo.FooException < aws.sdk.kotlin.foo.SomeException

This would allow customers to catch exceptions "at a distance" and distinguish which service was at fault.

Note: The Java V2 SDK does it this way.