v0.23.0

Introduce shutdown context, [app.Telemetry.ShutdownContext()].

This context should be used as explicit trigger of grafecul shutdown instead of
using base context.

Now, base context (ctx of Run function) can be used during shutdown for pending
work, i.e. pending requests or http server shutdown process, because base context
is not cancelled while in grafecul shutdown state.

Base context will be eventually shut down on timeout if graceful shutdown fails, so
previous behaviour is kept.