Outdated documentation of gcp_compute_forwarding_rule_info

https://docs.ansible.com/ansible/latest/collections/google/cloud/gcp_compute_forwarding_rule_info_module.html#return-resources/target

`target` variable is described as string which is not true. It is a dictionary with `selfLink` key - similar to what we have in `backendService`.

Please verify if it needs to be corrected in other modules as well.

Start with the linked gcp_compute_forwarding_rule_info documentation at return-resources/target and compare its description with backendService. Check related Google Cloud module return fields for the same type, then update the affected documentation so target is documented as a dictionary with a selfLink key and verify the other modules are accurate.

Written by the indexing model from the issue text.