Improve error messages for api failures

Current error messages for SCIM api failures/Google API/IdentityStore api are raw http errors. Whilst accurate they don't aid debugging, add helper functions to interpret protocol errors to give the user guidance on why the error is likely to have occurred.

For example a 401 for the SCIM api is likely to relate to a bad or expired token.

Start by locating the error-handling entry points for the SCIM API, Google API, and IdentityStore API, where raw HTTP errors are currently surfaced. Define helper behavior for interpreting protocol failures, including guidance that a SCIM 401 may indicate a bad or expired token; done means users receive actionable explanations instead of only raw errors.

Written by the indexing model from the issue text.