Reconcile templates and generated files + add nightly templates

[mikaelarguedas]

The source and nightly images started diverging significantly from the templates, and the nightly-rmw* images dont have a template of their own.

New snppets:

• setup up colcon mixin and metadata
• test that pytest is found

Templates now take env_before and env_after to pass env vars that the template should define

diff after this PR with images that will land on master

diff --git a/ros2/nightly/nightly/Dockerfile b/ros2/nightly/nightly/Dockerfile
index a04e35c..c2a7bc5 100644
--- a/ros2/nightly/nightly/Dockerfile
+++ b/ros2/nightly/nightly/Dockerfile
@@ -105,15 +105,9 @@ RUN . /opt/ros/$ROS_DISTRO/setup.sh \
       rti-connext-dds-5.3.1" \
     && rm -rf /var/lib/apt/lists/*
 
-# FIXME Remove this once rosdep detects ROS 2 packages https://github.com/ros-infrastructure/rosdep/issues/660
-# ignore installed rosdep keys
+# setup environment
 ENV ROS_PACKAGE_PATH /opt/ros/$ROS_DISTRO/share
 
-# FIXME Remove this once ament_export_interfaces respects COLCON_CURRENT_PREFIX https://github.com/ament/ament_cmake/issues/173
-#Workaround hard coded paths in nightly tarball setup scripts
-ARG UPSTREAM_CI_WS=/home/jenkins-agent/workspace/packaging_linux/ws
-RUN mkdir -p $UPSTREAM_CI_WS && ln -s /opt/ros/$ROS_DISTRO $UPSTREAM_CI_WS/install
-
 # setup entrypoint
 COPY ./ros_entrypoint.sh /

I kept thos manual changes as they are expected to be temporary and dont belong in the tmeplate. Can be added to the templates if preferred