add command line argument for passing extra args to gz sim

[M1chaelM]

This PR adds the extra_gz_args option to competition.launch.py and passes it through to gz sim. We had something similar in VRX classic so we could use gazebo options without having to implement command line arguments for all of them. (There might be a cleaner way to do this; if so please advise.)

The immediate reason for doing this is so we can use gz sim's recording functionality, which we need to get playback working.

To test

Try passing some arguments through to gz sim:

ros2 launch vrx_gz competition.launch.py headless:=false world:=stationkeeping_task extra_gz_args:="--record_period 0.01 --record_path $HOME/.gz_sim_arg_test --log_overwrite"

Check that logs are written to $HOME/.gz_sim_arg_test.

Bonus: adding support for "paused" argument. To test:

ros2 launch vrx_gz competition.launch.py paused:=true world:=stationkeeping_task

The simulation should start in a paused state.

[caguero]

Works as expected.