feat(rpc): add protocol config rpc endpoint

[bowenwang1996]

Add EXPERIMENTAL_protocol_config rpc endpoint that returns the protocol config given some block, since protocol config can change after genesis due to protocol upgrades. This will allow users to get the up-to-date protocol-level configs. Fixes #3918.

Test plan

test_protocol_config_rpc

[frol]

We need to make sure that dates, u64-like types (BlockHeight) are serialized as strings due to JSON numbers limitation.

[bowenwang1996]

I believe it is. For example,

nearcore/neard/res/genesis_config.json

Line 3 in 3ad75b5

"genesis_time": "1970-01-01T00:00:00.000000000Z",

[bowenwang1996]

@frol do you think we should deprecate EXPERIMENTAL_genesis_config (make it an alias to EXPERIMENTAL_protocol_config)? Or should we introduce EXPERIMENTAL_protocol_config separately in near-api-js? If we do the latter, we also need to make sure that wallet uses the new endpoint.

[frol]

@bowenwang1996 Good point. While the naming geneis_config implies that it should be genesis config, I think it makes sense to actually return the latest runtime config since that is what most of the users wanted to have in the first place; thus, I think we should go with the alias 👍

[frol]

Well, on the second thought, it would not be sane to expose the latest protocol config under genesis_config endpoint, and it is better to address the issue on near-api-js level (add deprecation note on the method, and use EXPERIMENTAL_protocol_config({"sync_checkpoint": "genesis"}) explicitly). I will take it from here.

[bowenwang1996]

Well, on the second thought, it would not be sane to expose the latest protocol config under genesis_config endpoint, and it is better to address the issue on near-api-js level (add deprecation note on the method, and use EXPERIMENTAL_protocol_config({"sync_checkpoint": "genesis"}) explicitly). I will take it from here.

Thanks @frol !

[frol]

Just for the reference, near-api-js support is coming: near/near-api-js#508