Previously we wouldn't notify when a channel moves into state
"CHANNELD_AWAITING_LOCKIN", as this is the original state (so there's
no movement btw states). This meant that it's impossible to track when a
channel's commitment txs have been exchanged and we're waiting for
onchain confirmation.
It's useful to have notice of this initialization though, all in one
place so that the `channel_state_changed` notification can successfully
track the entire lifecycle of a channel, from inception to close.
Note that for v2 "dual-funded" channels, we already notify at the same place, at
"DUALOPEND_AWAITING_LOCKIN" (the initial state for a dualopend channel
is "DUALOPEND_OPEN_INIT" -- this is the only state we don't get notified
at now...)
Changelog-Added: Plugins: `channel_state_changed` now triggers for a v1 channel's initial "CHANNELD_AWAITING_LOCKIN" state transition (from prior state "unknown")
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