matrix.hackerspace.pl: add secret appservice-irc mappings

These contain a channel key for a secret channel.

We also had to migrate the appservice-irc config to a secret.

Change-Id: I92c7cdf9679f65d9e655e22d690cef2e83180135
diff --git a/app/matrix/matrix.hackerspace.pl.jsonnet b/app/matrix/matrix.hackerspace.pl.jsonnet
index 1478401..ce42de7 100644
--- a/app/matrix/matrix.hackerspace.pl.jsonnet
+++ b/app/matrix/matrix.hackerspace.pl.jsonnet
@@ -51,6 +51,7 @@
                         },
                         servers+: {
                             "irc.freenode.net"+: {
+                                mappings+: import "secrets/plain/appservice-irc-freenode-mappings.jsonnet",
                                 ircClients+: {
                                     maxClients: 150,
                                 },