matrix2tsv: anonymize the content of the messages

bin/matrix2tsv

@@ -15,5 +15,6 @@
 # Select the three fields we need, replacing the sender address by its number
 # and output everything as a TSV.
 | .messages[]
-| [.origin_server_ts, $senders[.sender], .content.body]
+| (.content.body | gsub("<@\\S+:\\S+>"; "<******>")) as $body
+| [.origin_server_ts, $senders[.sender], $body]
 | @tsv