Feature/gateway direct stats

[neacsu]

Description

Add an opt-in flag for gateways that enables them to report the number of active inboxes they serve

Closes: #2032

Testing

1. Run a native client and a network requester that has a whitelist on localhost
2. On the same machine as 1), start the statistics service provider
3. Init and run a gateway. Use the --enabled-statistics true and --statistics-service-url $URL options, where $URL is a the address and port of the running statistics service from 2)
4. Watch how inbox statistics are being gathered in the $NYM_DIR/service-providers/network-statistics/db.sqlite. You can also query the data from the statistics machine:

curl -d '{"since":"2022-06-16T00:00:00.000000+00:00", "until":"2022-06-17T00:00:00.000000+00:00"}' -H "Content-Type: application/json" -X POST http://[STATS_MACHINE_ADDR]:8090/v1/all-statistics | json_pp

Checklist:

• added a changelog entry to CHANGELOG.md