Staging for additional to Nav2 project

[SteveMacenski]

• [x] Feedback from 2-3 users happy with performance
• [x] Rename for Nav2 naming conventions (nav2_mppi_controller)
• [x] Add to metapackage list
• [x] Add documentation page on website https://github.com/ros-planning/navigation.ros.org/pull/378
• [x] Add to plugins list https://github.com/ros-planning/navigation.ros.org/pull/378
• [x] Add to migration guide https://github.com/ros-planning/navigation.ros.org/pull/378
• [x] Add to Discourse announcement
• [x] Transfer tickets: Log-Normal distribution + Zero-mean + SMPPI + Acceleration characteristics

[SteveMacenski]

@artofnothingness I'm staging MPPI for Nav2 in https://github.com/ros-planning/navigation2/pull/3350

Very close to finishing this!

[SteveMacenski]

Continuing the staging check list in that PR