Refactor non-default sealing

[kalaninja]

• fix(service): confusing message when node starts (output the actual sealing method being used)
• refactor: how the sealing mode is passed into runtime
• feat: finalization for instant sealing

New sealing mode instant-finality is added to the cli (kudos to @tdelabro ) for command parsing:

enum Sealing {
  Manual,
  Instant,
  InstantFinality,
}

Internally sealing mode is represented with the following domain model:

enum SealingMode {
    #[default]
    Default,
    Manual,
    Instant {
        finalize: bool,
    },
}

let (command_sink, commands_stream) = mpsc::channel(1000); is adjusted to create for SealingMode::Manual only.

Closes #1144

[d-roak]

Hey @kalaninja, thanks ser !
Can u just had an entry to the changelog pls

[kalaninja]

@tdelabro @d-roak

NOTE: By default substrate doesn't finalize blocks with instant sealing. It is hardcoded
I can implement a workaround if needed, but I don't know what behavior is needed (if needed):

• always finalize
• add cli switch, e.g. --sealing=instant --finalize=true

[kalaninja]

As discussed with @d-roak I've added support for block finalization when instant sealing is used.

[tdelabro]

Good for me as soon as you address oak last comment