Rename message::Value

[rukai]

I chose ShotoverValue but maybe something like GenericValue or MessageValue could work?

[conorbros]

I prefer MessageValue because I imagine a transform developer interacting with Message and MessageValue better than Message and ShotoverValue but isn't a big deal so LGTM.

[rukai]

Yeah, after thinking about it, I agree, MessageValue does sound better.
ill swap to that.

[benbromhead]

I'm ok with MessageValue, but something like DatastoreValue is more descriptive (e.g. it is a value from the datastore)

[rukai]

It is currently used in cases the value didnt come from a datastore, so atm MessageValue makes more sense.
Although we might want to remove those cases in the future and then DatastoreValue would end up a better name.