export full database over network

[mleku]

it is already quite simple to feed a collection of events to a relay, half of the code already exists in the export/import and ingestr but to cleanly pull the entire database over the network while hot will be an important disaster prevention feature

the owners prescribed in the relay configuration will be able to send a request with an empty filter that will return every event in the database

a small tool that sends such requests and receives the results and optionally writes to .jsonl file, and can also read a .jsonl file and push all of the events in it to the relay while it is live, in both directions using the owner authentication to permit this backup/restore functionality

this is not high priority but should be completed for MS3