Add support to `get_content` in Ansible `gcp_storage_object`

From GoogleCloudPlatform/magic-modules#2427

> Similar to [gc_storage_module](https://docs.ansible.com/ansible/latest/modules/gc_storage_module.html) `get_str` mode.
> Since [the recommended way of storing secrets](https://cloud.google.com/kms/docs/store-secrets) is using GCS as some kind of parameter / secret store this would be a useful use case as I wouldn't want to either leave "temporary" files behind or dealing with clean up afterwards when that's simply unnecessary.

Start by locating the Ansible gcp_storage_object entry point and reviewing the linked gc_storage_module get_str mode and cited GCS secret-storage guidance. Done means supporting get_content for GCS-backed values without leaving temporary files or requiring cleanup.

Written by the indexing model from the issue text.