Update to handle core `v1.25` changes

Closes https://github.com/weaviate/typescript-client/issues/125 without significant refactoring required; builder pattern is easily forward compatible
Closes https://github.com/weaviate/typescript-client/issues/126 by the addition of new types and classes for providing subsearch arguments and mapping them to GQL strings
Closes https://github.com/weaviate/typescript-client/issues/136 by introducing TenantsExists builder and handling the successful 200 response appropriately

weaviate / typescript-client