Added service endpoint for ping_modem in tdma_advanced. added topic for changing auto ping_modem_src

New Features / Improvements

• Added service endpoint of an existing type ros_acomms_msgs/PingModem.srv to tdma_advanced (this was previously only handled by the modem driver. Now we can do the same service request in-band with tdma).
  • when service is called from tdma/ping_modem rather than ping_modem, the ping request will go out in the next active slot where nav pings are allowed
  • the service handler in tdma_advanced will use the cycle_duration OR request.reply_timeout (whichever is larger) to set a max timeout
  • the tdma_advanced service will appear to be "hung" while waiting on ping_modem reply. This service handles 1 ping at a time and does not have the safety gating auto ping does. This allows clients to use ping_modem as normal but IN tdma.
• Can now change the auto ping_modem_src with a topic for tdma_advanced (and child types)
  • topic: name: ~change_auto_ping_modem_src type: std_msgs/UInt8. publish message on this topic and auto ping will use new src. Also sets rosparam server with new value and invalidates dynamic reconfigure cache.
• Added CI for all new features (and some old):
  • change_auto_ping_modem_src feature
  • tdma/ping_modem service
  • ping_modem service