chore(protocol): minor cleanup of ClusterConfig messages; remove DisableTempIndexes option (#10202)

This makes a couple of backwards compatible changes to the
ClusterConfig:

- Remove the `ignore_permissions` and `ignore_delete` booleans which
we've never read or used for anything
- Remove the `disable_temp_indexes` boolean and option entirely. We did
use this one, and about 1% of users have set the option. The only thing
it does is inhibits sending of periodical DownloadProgress messages
while downloading data, which is a minuscule bandwidth optimisation
given that we're already sending data at the time.
- Change the `read_only` boolean (which indicated send-only folders) to
an enum `FolderType`, where the values zero and one match the existing
usage. Again, we don't actually use this value, but I can see that we
might want to and then it makes more sense for it to be more
comprehensive.
- Change the `paused` boolean to an enum `StopReason`, where zero
indicates not stopped and one indicates paused, exactly the same wire
representation as previously but leaves space for additional stop
reasons (errors etc).

lib/ur/usage_report.go

@@ -247,9 +247,6 @@ func (s *Service) reportData(ctx context.Context, urVersion int, preview bool) (
 			if cfg.DisableSparseFiles {
 				report.FolderUsesV3.DisableSparseFiles++
 			}
-			if cfg.DisableTempIndexes {
-				report.FolderUsesV3.DisableTempIndexes++
-			}
 			if cfg.FSWatcherEnabled {
 				report.FolderUsesV3.FsWatcherEnabled++
 			}