- Add new command to the cli/node: `serveapi` that alows serving the API just
by connecting to the PostgreSQL database. The mode flag should me passed in
order to select whether we are connecting to a synchronizer database or a
coordinator database. If `coord` is chosen as mode, the coordinator
endpoints can be activated in order to allow inserting l2txs and
authorizations into the L2DB.
Summary of the implementation details
- New SQL table with 3 columns (plus `item_id` pk). The table only contains a
single row with `item_id` = 1. Columns:
- state: historydb.StateAPI in JSON. This is the struct that is served via
the `/state` API endpoint. The node will periodically update this struct
and store it int he DB. The api server will query it from the DB to
serve it.
- config: historydb.NodeConfig in JSON. This struct contains node
configuration parameters that the API needs to be aware of. It's updated
once every time the node starts.
- constants: historydb.Constants in JSON. This struct contains all the
hermez network constants gathered via the ethereum client by the node.
It's written once every time the node starts.
- The HistoryDB contains methods to get and update each one of these columns
individually.
- The HistoryDB contains all methods that query the DB and prepare objects that
will appear in the StateAPI endpoint.
- The configuration used in for the `serveapi` cli/node command is defined in
`config.APIServer`, and is a subset of `node.Config` in order to allow
reusing the same configuration file of the node if desired.
- A new object is introduced in the api: `StateAPIUpdater`, which contains all
the necessary information to update the StateAPI in the DB periodically by
the node.
- Moved the types `SCConsts`, `SCVariables` and `SCVariablesPtr` from
`syncrhonizer` to `common` for convenience.
