app/matrix/appservice-irc: implement passwordEncryptionKey

This allows people to save their NickServ passwords into bridge's
storage. Obviously nobody should trust us tho.

Change-Id: I2afe9e5215cd8f7419e9eab8183789df13e21aac
diff --git a/app/matrix/matrix.hackerspace.pl.jsonnet b/app/matrix/matrix.hackerspace.pl.jsonnet
index 8ca94f4..f150f6d 100644
--- a/app/matrix/matrix.hackerspace.pl.jsonnet
+++ b/app/matrix/matrix.hackerspace.pl.jsonnet
@@ -53,6 +53,7 @@
                         },
                     },
                 },
+                passwordEncryptionKeySecret: "appservice-irc-password-encryption-key",
             },
         },
         "telegram-prod": telegram.AppServiceTelegram("prod") {