sqldb: init

This implements a basic driver for using Postgres, SQLite or MySQL as storage engine for nostr-database. Uses async Diesel as driver and Diesel migrations to set up the schema.

Pull-Request: #835
Pull-Request: #855
Signed-off-by: Yuki Kishimoto <yukikishimoto@protonmail.com>

Author: tompro

CHANGELOG.md

@@ -87,6 +87,7 @@
 - mls-memory-storage: add an in-memory implementation for MLS ([JeffG] at https://github.com/rust-nostr/nostr/pull/839)
 - mls-sqlite-storage: a sqlite implementation for MLS ([JeffG] at https://github.com/rust-nostr/nostr/pull/842)
 - mls: add new crate for implementing MLS messaging ([JeffG] at https://github.com/rust-nostr/nostr/pull/843)
+- sqldb: add `nostr-sqldb` crate ([Thomas Profelt] at https://github.com/rust-nostr/nostr/pull/835)
 - pool: add relay monitor ([Yuki Kishimoto] at https://github.com/rust-nostr/nostr/pull/851)
 - sdk: add `Options::pool` ([Yuki Kishimoto])
 - relay-builder: add support for NIP-70 protected events ([Yuki Kishimoto] at https://github.com/rust-nostr/nostr/pull/875)