feat: adds state change cause and message

This adds a `state_change` 'cause' to a channel.
A 'cause' is some initial 'reason' a channel was created or closed by:

  /* Anything other than the reasons below. Should not happen. */
  REASON_UNKNOWN,
  /* Unconscious internal reasons, e.g. dev fail of a channel. */
  REASON_LOCAL,
  /* The operator or a plugin opened or closed a channel by intention. */
  REASON_USER,
  /* The remote closed or funded a channel with us by intention. */
  REASON_REMOTE,
  /* E.g. We need to close a channel because of bad signatures and such. */
  REASON_PROTOCOL,
  /* A channel was closed onchain, while we were offline. */
  /* Note: This is very likely a conscious remote decision. */
  REASON_ONCHAIN

If a 'cause' is known and a subsequent state change is made with
`REASON_UNKNOWN` the preceding cause will be used as reason, since a lot
(all `REASON_UNKNOWN`) state changes are a subsequent consequences of a prior
cause: local, user, remote, protocol or onchain.

Changelog-Added: Plugins: Channel closure resaon/cause to channel_state_changed notification

wallet/db_postgres_sqlgen.c

@@ -1660,4 +1660,4 @@ struct db_query db_postgres_queries[] = {
 
 #endif /* LIGHTNINGD_WALLET_GEN_DB_POSTGRES */
 
-// SHA256STAMP:8a260050ced7606fcad6e15df51a42a442f3119ad82d8e86fa2d348a2a45ee1a
+// SHA256STAMP:bb84a713ee593a4ac2441ae971851f3b466e8c2bd6cf3cbf6261f3d4d0fb803d