Block query in GraphQL

[psteckler]

Add a query block in GraphQL that takes a stateHash string, and returns a block with that state hash, using the same format as the blocks returned by bestChain.

Closes #7404. Well, maybe, it doesn't support querying by height. Should we provide that as a separate query? I think we'd need to linear search through all breadcrumbs to support that, or add additional indexing to support such a query.

[bkase]

We do want height as another argument in my opinion: Yes it's a linear search on the best-chain but the best-chain size is capped at k=290 and walking the 290 chain won't be expensive. (feel free to add it in a follow-up PR if you want though)

[bkase]

Since there are multiple places where a failure can be introduced in the processing of this query -- can you make this a result_field instead and provide proper error messages for each of the places where we (currently) are binding over the option? Then a consumer can understand why it's failing.

[psteckler]

@bkase Do you mean a distinct query, like blockByHeight, or that height should be an additional optional argument?

[bkase]

Looks great! But yes please make stateHash nullabke and height another nullable parameter. And just error if both are null (this is a convention in graphql apis).

the height you can follow up with, but could you make the stateHash parameter nullable now so we don’t need to break compatibility when you add height.