Create Issue and PR formats / templates

[SteveMacenski]

GitHub allows you to do this (https://github.com/ros-planning/navigation2/community) and its useful so when others want to file tickets or PRs, we can create a recommended format or reminders to include important information.

Intel's librealsense2 repo has a good example of such a template (https://github.com/IntelRealSense/librealsense/issues/new)

I don't see a way to create a PR template, but I've created an issue template based on OSRF's template for RCLCPP.

It is pretty generic, but I figure we can add to it as we go along.

The Realsense one seemed a bit too specific to their stuff

[SteveMacenski]

Definitely. Start with something and add more as we go.

I can lob out a starter PR template then