planner support for configuring SP images/slots

[davepacheco]

This ticket involves:

• Augmenting the blueprint structures (db and in-memory) to represent configuration for SP images and slots. The details here are TBD but presumably we need to say something about the fact that one or both SP slots should have a particular image in it.
• Updating the planner to populate these fields when appropriate.

As we've discussed with zones: we probably want values for these fields that mean the equivalent of "unconfigured", or "make no changes to what's there". That is, I think we don't want to just backfill these with values from inventory because those will be wrong after the next mupdate. We want production systems to have values for these that mean "as-is, don't touch it" until we actually switch to blueprint-driven update.

[davepacheco]

Much of the work here is done in #8261. I hope it will be easy to integrate that into the planner once #8024 lands.