Expose GTO's model version in FastAPI's interface.json

[aguschin]

Follow-up for #664. Sometimes it's desired to store predictions along with the specific model version that returned those predictions. There are at least two ways to support that in MLEM:

1. Return model version in prediction - then what's returned will be a json like {"prediction": [0.4, 0.6], "version": 0.1.3}. I've seen some generic ML frameworks doing this IIRC.
2. Return it in interface.json - we already have MLEM version there, so adding model version looks logical

Regarding how we get this info into the service. Again, there are two approaches:

1. Add it at mlem.api.save
2. Allow to specify it when building server

First seems more reasonable to me. Since this will require some under-the-hood integration with GTO, I'd do this after #664 - which have the same decision to make.

fyi @omesser

[aguschin]

For the record, I'm going to take 2nd option (Return version in interface.json).

And it looks like I need iterative/gto#335 completed first to support this in MLEM.

[aguschin]

UPD: getting the version at mlem.api.save doesn't work since at this moment the commit doesn't exist, not mentioning the right GTO git tag. So it should be read once you build a server.