Mega Feature: Versioning and rollout of changes to ResourceGraphDefinitions

[matthchr]

This mega feature exists to track the requests for versioning/rollouts as there are multiple.

Note: This issue is probably too big to be even a single mega feature and likely needs to be split into multiple, but trying to keep it simple for now given how many separate issues we already have tracking these features.

We need to answer the following questions:

1. When an RGD changes how are those changes rolled out to the RG instances? Can the RGD author control how updates are applied? Or can the instance author control?
2. How will rollbacks happen?
3. When a breaking change to the RGD inputs is made, what happens? - Current plan is to block breaking changes.

[matthchr]

Proposed KREP-006: Propagation Control is related to this topic