Add support for automatic discovery range

[civerachb-cpr]

Write the ROS_AUTOMATIC_DISCOVERY_RANGE and ROS_STATIC_PEERS envars to setup.bash

Sample configuration (not necessarily useful, but syntactically valid):

system:
  ros2:
    middleware:
      automatic_discovery_range: subnet  # one of subnet, localhost, system_default, or off
      static_peers:  # array of hostnames and/or IP addresses
        - 192.168.131.1
        - 192.168.131.2
        - 192.168.131.100

result in setup.bash:

export ROS_AUTOMATIC_DISCOVERY_RANGE=SUBNET
export ROS_STATIC_PEERS="192.168.131.1;192.168.131.2;192.168.131.100"

Part of RPSW-2778.

[mergify]

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