Support automatic semver upgrades

[thedodd]

The initial release will require that the image repo and tag be hard-coded in the Stream CR. As part of this feature, we will make that block optional, and when omitted, the operator will manage the image versions and perform automatic upgrades based on maintenance windows.

• fetch tags of hadron-stream, and determine latest release per semver compat group. Pass in latest release to StatefulSet builder.
• Operator should check for latest tags periodically.