Add ability to request a block via its hash

[evan-forbes]

We should add the ability to query a block by its hash via grpc. Currently, we can only easily by its height.

To close this issues, introduce a new grpc method that uses a new index hash: height, to first look up the height and then look up the block based on its height.

ref celestiaorg/celestia-app#3421 (comment)

[cmwaters]

I don't think this issue belongs in this repo. We discussed having the gRPC server as a service in celestia-app or at least extending the existing interface in our cosmos-sdk although I would prefer to keep this in celestia-app

[Eoous]

I think it's no necessary and difficult to have gRPC service in celestia-app or cosmos-sdk.

Looks like that we can merge gRPC service from cometbft for celestia-core: cometbft/cometbft#2693

[rach-id]

Does #1513 closes this too? or something else is needed