core/api-spec: remove get actions in favor of list actions
core/api-spec: remove get actions in favor of list actions

This removes the need for separate `GET` asset/transaction/account
endpoints, and instead enables them through CHQL queries to the`LIST`
endpoints.

For the first phase, we will only support querying a single transaction/asset/account (e.g. `transaction_id = $1`).

We will NOT support batch queries by ID (e.g. `transaction_id IN [$1, $2]`).

Closes chain/chainprv#1205.
Reviewers: da39a3ee5e6b4b0d3255bfef95601890afd80709@kr




chain/chain,chain/chain,chain/chain,chain/chain,chain/chain,chain/chain