Revert "disable EnablePublicChannelsMaterialization by default (#9418)" (#9427)

This reverts commit 5786b0d6d5, now that
the feature is safe to enable by default.

model/config.go

@@ -687,7 +687,7 @@ func (s *SqlSettings) SetDefaults() {
 	}
 
 	if s.EnablePublicChannelsMaterialization == nil {
-		s.EnablePublicChannelsMaterialization = NewBool(false)
+		s.EnablePublicChannelsMaterialization = NewBool(true)
 	}
 }