Be able to receive a PoseWithCovarianceStamped message as a localization prior.

[nicolaslauzon]

Why

When you load a map, you need to specify the pose manually. This is hard if not impossible to get right.

With this subscriber, we could use the initial pose arrow in foxglove and rviz to give a good guess after loading a map.

This is way more instinctive.

This feature would be especially usefull when running multiple DRIVE iterations. Right now the workflow is to remap between each of them.

PoseWithCovarianceStamped

Notes after talking to Simon-Pierre :

1. We could do a node that publishes the new map with a movable marker. Then you can visually align with the current PCL and then press a button to load the map into the mapper with the alignement pose.

2. We could also have the ability to publish a pose anytime and then call a service with simply the map to load. This service would then query the last pose and use it for prior.