Support ROS 2 Jazzy (main backport)

[msz-rai]

This PR modifies FindRGL.cmake to support ROS2 Jazzy besides ROS2 Humble. It also introduced minor improvements:

• does not download RGL if metadata matches
  • makes cmake reload faster
  • enables using custom RGL binaries easier
• changes directory where RGL is downloaded (CMAKE_BINARY_DIR instead of CMAKE_SOURCE_DIR)
  • good practice is to make the source directory read-only
  • resetting cmake cache makes a true clean build of the gem (with a new RGL download)