[server] Use proper graceful shutdown

[agnesoft]

Graceful shutdown is no longer available in hyper 1.0 and thus in axum 0.7. There is open issue for it to be re-added in hyper-utils: hyperium/hyper#2862

The new way of doing graceful shutdown is to manually implement the server (axum::serve method) and it also forces the choice to exclusively use http1(.1) or http2. Neither is very appealing with the latter being a deal breaker.

Current implementation simply cancels the server possibly causing data loss for clients. The databases even for open transactions will be ok (on drop the transactions get aborted and data integrity restored due to write ahead log (WAL) ).

Two options:

1. Prevent client data loss by tracking open requests and stopping serving new ones (probably in the logger layer?) when shutdown is invoked. Let the main cancel the server as normal once the ongoing requests reach 0.

2. Use proper graceful shutdown when it becomes available in hyper.

[agnesoft]

Is being fixed by:

hyperium/hyper#3457 (merged)
hyperium/hyper-util#66 (merged)
tokio-rs/axum#2398 (merged)