Action to attach and detach persistent disks to running GCE instance

##### SUMMARY

Please add support for attach/detach persistent disk from running GCE instance. A related bug is discussed in issue https://github.com/ansible-collections/google.cloud/issues/193

##### ISSUE TYPE
- Feature Idea

##### COMPONENT NAME

google.cloud.gcp_compute_instance would be a good place to add the attach/detach actions.

##### ADDITIONAL INFORMATION

It would be nice to be able to detach a persistent disk from one running instance and attach it to another running instance. This is good for doing DR testing use case.

```yaml
- name: detach persistent disk
gcp_compute_instance:
name: test-vm
disks:
- detach: true
source: "{{ disk }}"
```

```yaml
- name: attach persistent disk
gcp_compute_instance:
name: restore-test-vm
disks:
- attach: true
source: "{{ disk }}"
```

Start with the google.cloud.gcp_compute_instance component named in the issue and review related issue 193. Compare the requested attach and detach examples, then verify that persistent disks can be detached from one running instance and attached to another running instance for the DR testing use case.

Written by the indexing model from the issue text.