Allow json content in place of a file for service_account_file

##### SUMMARY

Ability to use json content instead of requiring an actual file for credentials (service_account_file). This allow us to retrieve secrets from HashiCorp Vault or other external vault services, or passing it as an input at runtime.

##### ISSUE TYPE
- Feature Idea

##### COMPONENT NAME
The applies to any modules, roles in this collection that make use of service_account_file

##### ADDITIONAL INFORMATION
A use case would be allow the key file to be stored in HC Vault or other vault like services, and retrieved at run time. This allow the key file to be updated and managed by a different team.

Another use case is running playbooks in AWX and using the Survey feature to ask user to post the json content of key. This allow us to use same playbook for different teams using different GCP projects and having different keys.

Start by locating the modules and roles in the google.cloud collection that use service_account_file, then review how they currently load credentials. Done means those entry points can accept JSON credential content as well as a file path, while retaining existing file-based behavior and covering the supported use cases with tests.

Written by the indexing model from the issue text.