Update debian systemd service to use Type=notify (#8169)

This ensures systemctl start matrix-synapse returns only after synapse
is actually started, which is very useful for automated deployments.

Fixes #5761

Signed-off-by: Dexter Chua <dec41@srcf.net>

debian/changelog

+matrix-synapse-py3 (1.19.0ubuntu1) UNRELEASED; urgency=medium
+
+  * Use Type=notify in systemd service
+
+ -- Dexter Chua <dec41@srcf.net>  Wed, 26 Aug 2020 12:41:36 +0000
+
 matrix-synapse-py3 (1.19.0) stable; urgency=medium
 
   [ Synapse Packaging team ]

debian/matrix-synapse.service

@@ -2,7 +2,7 @@
 Description=Synapse Matrix homeserver
 
 [Service]
-Type=simple
+Type=notify
 User=matrix-synapse
 WorkingDirectory=/var/lib/matrix-synapse
 EnvironmentFile=/etc/default/matrix-synapse