DOCUMENTATION: Add Exception Documentation for C# Library: CompletionClientValidationException, CompletionClientDependencyException, and CompletionClientServiceException

[mabroukmahdhi]

@hassanhabib @BrianLParker @cjdutoit @TehWardy @ElbekDeveloper
What do you think about this? Do we need here a documentation for what kind of Exceptions can be thrown?

Exmaple:

Exception Name	When it will be thrown
CompletionClientValidationException	This exception is thrown when a validation error occurs while using the completion client. For example, if required data is missing or invalid.
CompletionClientDependencyException	This exception is thrown when a dependency error occurs while using the completion client. For example, if a required dependency is unavailable or incompatible.
CompletionClientServiceException	This exception is thrown when a service error occurs while using the completion client. For example, if there is a problem with the server or any other service failure.

[hassanhabib]

@mabroukmahdhi I think it's a great idea.