[Epic] Backup ownership and sharing

[rosskukulinski]

User Stories

As a cluster administrator, I would like to be able to safely backup from Cluster A and restore into Cluster B. E.g.

• Production cluster backing up hourly, staging cluster restoring from the production backups to maintain a "real-world" environment
• Production cluster A backing up, hot-standby Production Cluster B restoring on a regular basis

Features

• Add/enforce ownership of backup locations
• Resolve naming conflicts when importing backups from multiple clusters
• Update FAQ re: sharing buckets

Non-Goals

• Integration with IAM or other authentication/authorization systems

Notes

This behavior is currently supported through a restoreOnly mode which is prone to user error.