Library documentation typo on import

[Hernan Garcia]

Documentation states to import library as follows
```
from charms.sunbeam_sunbeam_identity_service_operator.v0.identity_service import IdentityServiceRequires
```

But it should be corrected to
```
from charms.sunbeam_keystone_operator.v0.identity_service import IdentityServiceRequires
```

[Hemanth Nakkina (hemanth-n)]

This has been fixed as part of this commit [1].

This change is yet to be released onto charmhub.
Marking this as Fix committed.

[1] https://opendev.org/openstack/charm-keystone-k8s/commit/9988c3e2d3773a9918f5e10f6a860fcb6f102002