Expand to include GCP

Is your feature request related to a problem? Please describe.
Currently the wrapper is focused on Azure and vSphere image building and only sets up the requirements for those.

Describe the solution you'd like
I would like to see the options expanded to include options to build GCP images.

Describe alternatives you've considered
Alternatives would be to manually create the required files to build GCP images using the Tanzu image builder documentation.

Additional context
This feature is to be able to expand the current scope to aid users in setting up requirements to build images. Ultimately the imagebuild_wrapper leverages the docker container to do the actual work, but there are requirements for settings to be able to connect to destination.