Add GCP Data Storage

[TildeWill]

Description

Situation:
Our company uses GCP, now AWS nor Azure. Using GCP buckets is the easiest (only?) way to share a persistent file system between server nodes for us. Right now, when we deploy Structurizr we have to back up the container, get the file system for Structurizr, then transfer them to the new container. Having GCP support would let those files live independently of the software and would let us scale our servers too.

Priority

I'm a Structurizr Patreon member (add details below or send a message on Patreon with a link to the issue)

More information

I'm Will Read on Patreon. I would be willing to submit a PR if this is not a priority.