Add custom exception class to catalogue python package

[LavMatt]

User Story

As a developer
I want to add custom exception class to data-platform-catalogue
So that we have better defined errors for us and users

Value / Purpose

improve development and user experience

Useful Contacts

No response

User Types

No response

Hypothesis

If we raise an error via one of our client methods
Then we return enlightening information as to why

Proposal

No response

Additional Information

you can see example of how we currently handle errors here https://github.com/ministryofjustice/data-platform/blob/main/python-libraries/data-platform-catalogue/data_platform_catalogue/client/datahub/search.py#L80

Definition of Done

• add custom exception class to package
• make some tests for custom exceptions