Log when a channel is closed on startup due to stale ChannelManager

[TheBlueMatt]

This is one of the riskiest parts of our API from the perspective
of accidental force-closes - if users delay persisting the
ChannelManager much at all after a ChannelMonitor we may hit a
force-close after restart.

The fact that we don't log at all when this happens is criminal.

[codecov]

Codecov Report

Merging #1029 (5307b5e) into main (bee9a1e) will increase coverage by 1.56%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1029      +/-   ##
==========================================
+ Coverage   90.80%   92.37%   +1.56%     
==========================================
  Files          60       61       +1     
  Lines       31460    40551    +9091     
==========================================
+ Hits        28568    37459    +8891     
- Misses       2892     3092     +200     

Impacted Files	Coverage Δ
lightning-background-processor/src/lib.rs	95.58% <ø> (ø)
lightning/src/ln/channelmanager.rs	90.28% <100.00%> (+4.66%)	⬆️
lightning/src/ln/chanmon_update_fail_tests.rs	97.73% <0.00%> (-0.01%)	⬇️
lightning/src/lib.rs	100.00% <0.00%> (ø)
lightning/src/ln/features.rs	99.56% <0.00%> (+0.12%)	⬆️
lightning/src/ln/reorg_tests.rs	99.76% <0.00%> (+0.13%)	⬆️
lightning/src/ln/onion_utils.rs	95.21% <0.00%> (+0.29%)	⬆️
lightning-block-sync/src/http.rs	94.04% <0.00%> (+0.33%)	⬆️
lightning/src/chain/onchaintx.rs	94.66% <0.00%> (+0.47%)	⬆️
lightning/src/ln/msgs.rs	89.24% <0.00%> (+0.55%)	⬆️
... and 16 more

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[ariard]

ACK 05de81b

[TheBlueMatt]

Pushed a trivial wording clarification as suggested by @ariard. Compared to ACKs full diff is below, will merge after CI:

$ git diff-tree -U1 05de81bf 5307b5e8
diff --git a/lightning/src/ln/channelmanager.rs b/lightning/src/ln/channelmanager.rs
index bf19dc10..c5db4075 100644
--- a/lightning/src/ln/channelmanager.rs
+++ b/lightning/src/ln/channelmanager.rs
@@ -4962,3 +4962,4 @@ impl<'a, Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref>
 					// But if the channel is behind of the monitor, close the channel:
-					log_error!(args.logger, "A ChannelManager is stale compared to the current ChannelMonitor! The channel will be closed.");
+					log_error!(args.logger, "A ChannelManager is stale compared to the current ChannelMonitor!");
+					log_error!(args.logger, " The channel will be force-closed and the latest commitment transaction from the ChannelMonitor broadcast.");
 					log_error!(args.logger, " The ChannelMonitor for channel {} is at update_id {} but the ChannelManager is at update_id {}.",
$