fix(admin): log admin server exceptions and close admin socket

Admin server was crashing silently and requests hang indefinitely.
With this fix, we are now logging the admin server exceptions and also
close the socket afterwards so admin request don't hang.

Signed-off-by: Taimoor Zaeem <taimoorzaeem@gmail.com>

src/PostgREST/Observation.hs

@@ -23,6 +23,7 @@ import Protolude hiding (toList)
 
 data Observation
   = AdminStartObs Text
+  | AdminServerCrashedObs SomeException
   | AppStartObs ByteString
   | AppServerAddressObs Text
   | ExitUnsupportedPgVersion PgVersion PgVersion