Add additional GET RPC endpoints

[wileyj]

Problem: the stacks blockchain RPC interface for GET requests is limited compared the data exposed in bitcoin/etc and the rich data in Hiro's API.

With recent changes to the HTTP interface (https://github.com/stacks-network/stacks-core/tree/master/stackslib/src/net/api), it should be much easier to add more RPC endpoints to expose some generic data. Initially, i'm thinking something like:

• block data
• tx data
• address info

some comparable bitcoin-cli rpc commands:
getblockhash
getblock
getrawtransaction
gettxout

for the data exposed, i don't think it should be a requirement to be as detailed as the Hiro API - but i think should be enough to understand what is in a block, or what a tx is doing (as well as retrieving the block hash by a block height).

references:
bitcoin RPC:

• https://developer.bitcoin.org/reference/rpc/getblockhash.html
• https://developer.bitcoin.org/reference/rpc/getblock.html
• https://developer.bitcoin.org/reference/rpc/getaddressinfo.html
• https://developer.bitcoin.org/reference/rpc/getrawtransaction.html
• https://developer.bitcoin.org/reference/rpc/gettxout.html

Hiro API:

• https://hirosystems.github.io/stacks-blockchain-api//#tag/Blocks/operation/get_block_by_hash
• https://hirosystems.github.io/stacks-blockchain-api//#tag/Blocks/operation/get_block_by_height
• https://hirosystems.github.io/stacks-blockchain-api//#tag/Blocks/operation/get_block_by_burn_block_hash
• https://hirosystems.github.io/stacks-blockchain-api//#tag/Transactions/operation/get_transaction_by_id
• https://hirosystems.github.io/stacks-blockchain-api//#tag/Transactions/operation/get_raw_transaction_by_id

[jcnelson]

• We have getblock via GET /v2/blocks/{index-block-hash}.
• We have gettxout via GET /v2/accounts/{:address}

We can add an endpoint to get a sortition for a particular block height, which would be the equivalent of getblockhash.

We don't have our equivalent of txindex turned on by default, so getrawtransaction would be disabled by default. However, we could add this endpoint to serve whatever indexed transactions we have if the user enables txindex.

[8marz8]

@saralab Do you think this would be a good ticket for me to work on during my free cycles/after my current tickets are merged? If so, perhaps it could be further scoped with the help of @kantai and @jferrant to determine what would be most useful for Nakamoto.