RFC : Asynchronous / background tasks

[hartym]

A few applications requires background tasks, either delayed (for example, write queue for transactions), delayed until something is ready (for example, inserting users in database once the storage is ready), or scheduled (for example telemetry pings).

Different methods are used (for now) and this is a problem as such, there should be one and only one obvious way to do it.

Also, unmanaged asyncio tasks can be problematic, so there must be some standard way to manage them (that allows tearing down, including in tests, and maybe allowing to restart, log, etc.)