Added resourceState to the ObjectMetadata type

[jwngr]

The resourceState property is in the payload, just not in the type information.

@katfang - Can you confirm that the type should be string (meaning it will always be there) and not string? (meaning it is optional)?

[katfang]

Huh, well, that's an interesting question.

Right now, we want string.

But the eventual goal is to have different event types, and drop resourceState. This'll happen when we move onto GCS Pubsub. How terrible would it be to change it to string? when we introduce the new event types? (Where down the line does this come?

[jwngr]

How terrible would it be to change it to string? when we introduce the new event types?

Since this is now a public API and people are using it, we can't just change its behavior until the next breaking change. We can introduce a new property which can be used instead and deprecate resourceState, but we will need to backfill resourceState until we cut a new major version, else may break people's existing Cloud Functions.

It sounds like the string typing is correct for this property. I've also already added this property to our public reference docs here.