Microvm repo check if spec is the same

[richardcase]

Describe the solution you'd like:
When saving the microvm spec in the repo we need to check if there is actually an update to the spec or not. If nothing has changed, then we don't need to take any action.

Why do you want this feature:

If we currently try saving where there is no update then an error is returned.

Anything else you would like to add:

Easiest way is to SHA256 hash the content and compare it to the digest of the content in the containerd content store.