API implementation for fetching identities and update extern_uid

What does this MR do and why?

#227841 (closed) - Solves

Screenshots

How to reproduce.

Following curl commands can be used to test new API implementation

curl --location --request GET 'https://gdk.test:3443/api/v4/groups/33/saml/identities' \
--header 'PRIVATE-TOKEN: bMyzyngq8-Xa3eJFk5sW' \

curl --location --request PATCH 'https://gdk.test:3443/api/v4/groups/33/saml/4' \
--header 'PRIVATE-TOKEN: bMyzyngq8-Xa3eJFk5sW' \
--form 'extern_uid="5"' \
--form 'active="false"'