Install the optional dependencies into the debian package (#4325)

since #4298, the optional dependencies are no longer installed with a simple
`pip install .`, which meant that they were not being included in the debian
package.

The easy fix to that is dh_virtualenv --extras, but that needs dh_virtualenv
1.1...

debian/build_virtualenv

@@ -33,7 +33,8 @@ dh_virtualenv \
     --preinstall="lxml" \
     --preinstall="mock" \
     --extra-pip-arg="--no-cache-dir" \
-    --extra-pip-arg="--compile"
+    --extra-pip-arg="--compile" \
+    --extras="all"
 
 # we copy the tests to a temporary directory so that we can put them on the
 # PYTHONPATH without putting the uninstalled synapse on the pythonpath.

debian/control

@@ -5,7 +5,7 @@ Maintainer: Synapse Packaging team <packages@matrix.org>
 Build-Depends:
  debhelper (>= 9),
  dh-systemd,
- dh-virtualenv (>= 1.0),
+ dh-virtualenv (>= 1.1),
  lsb-release,
  python3-dev,
  python3,