Add conditional support for SCIM providers which do not offer /Schemas /ResourceTypes endpoints like AWS

[marcportabellaclotet-mt]

I would like to manage AWS SCIM with this scim2 library. AWS has some known limitations, and /schemas and /ResourceTypes endpoints are not available.

I would like the conditional option (if not yet done), to be able to bypass the missing /schemas and /resourcetypes read, and add some default values