Delay bridge startup to ensure Synapse is up

Bridges start matrix-synapse.service as a dependency, but
Synapse is sometimes slow to start, while bridges are quick to
hit it and die (if unavailable).

They'll auto-restart later, but .. this still breaks `--tags=start`,
which doesn't wait long enough for such a restart to happen.

This attempts to slow down bridge startup enough to ensure Synapse
is up and no failures happen at all.

roles/matrix-bridge-appservice-irc/templates/systemd/matrix-appservice-irc.service.j2

@@ -14,6 +14,9 @@ Type=simple
 ExecStartPre=-/usr/bin/docker kill matrix-appservice-irc
 ExecStartPre=-/usr/bin/docker rm matrix-appservice-irc
 
+# Intentional delay, so that the homeserver (we likely depend on) can manage to start.
+ExecStartPre=/bin/sleep 5
+
 ExecStart=/usr/bin/docker run --rm --name matrix-appservice-irc \
 			--log-driver=none \
 			--user={{ matrix_user_uid }}:{{ matrix_user_gid }} \