[Feature]: Block streaming endpoint

[polydez]

To whom is this feature for?

App developer

Why is is this feature needed?

For block indexer/explorer developers It might be useful to be able to obtain new blocks not by using polling, but connecting to a streaming endpoint and receive every new block once it is ready. This also can speed up consumer synchronization from the first block to current, if the blockchain has been running for a long time.

How is this feature used?

Developer requests blocks starting from the given number, this establishes streaming connection using native gRPC streaming support.

Anything else?

No response

[bobbinth]

I guess there are a couple of options here:

1. The endpoint takes the block_num as input and streams all blocks starting at that number until the current block.
2. The connection stays open and the user streams blocks as they are created.
3. (we could also combine the two).

I'm not sure about the complexities (and implications) of the second option - so, don't have a good sense which option we should go with.

Also, regardless of the option, we probably should think about some kind of DoS prevention mechanism as this endpoint can result in returning lots of data. This would probably be related to #52.