Adding ready to meet message

[tylerferrara]

A ROS service is available at /tb3_X/ready_to_meet, defined within coms/coms/srv/ReadyToMeet.srv:

# ReadyToMeet.srv
string robot_ip
bool status
---
bool is_ready

This service asks the robot_ip if it's ready for a meeting, returning bool is_ready. If the robot is unreachable, an error will be logged in /tb3_X/coms_debug while returning False.

You can also test this by running:

$ rostopic pub /tb3_0/coms_listening std_msgs/String "ready|192.168.0.2|true"

NOTE: This will not change any state, but only probe the other robot in the the logs.