Addition of base_footprint frame in TF tree

[ghost]

Description

The root frame of the current tf tree for the bot is base_link.

The following guideline is provided on the nav2 documentation on Setting Up The URDF

The base_footprint link is a virtual (non-physical) link which has no dimensions or collision areas. Its primary purpose is to 
enable various packages determine the center of a robot projected to the ground. For example, Navigation2 uses this link to 
determine the center of a circular footprint used in its obstacle avoidance algorithms. Again, we set this link with no 
dimensions and to which position the robot’s center is in when it is projected to the ground plane.

Maps pass through the bot with nav2 stack

Benifits

Although not a neccesecity, the addition of base_footprint enables the bot to work with nav2 stack out of the box as base_footprint is a default parameter in most cases.

A good example of this would be turtlebot3