Add ROS2 Launch Files to all relevant examples

[adeeb10abbas]

This PR adds launch files to all the examples that involve a visual (rviz) component. All the launch files were tested.

@EricCousineau-TRI for review, thanks!

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This change is 

[EricCousineau-TRI]

with a few small nits, thanks!

Reviewed 12 of 12 files at r1, all commit messages.
Reviewable status: all files reviewed, 4 unresolved discussions (waiting on @adeeb10abbas)

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drake_ros_examples/examples/hydroelastic/launch/hydroelastic_cc_launch.py line 6 at r1 (raw file):

from ament_index_python.packages import get_package_prefix
from ament_index_python.packages import get_package_share_directory
import os

nit (here and elsewhere) For imports, can you sort between (builtin, third-party), and then alpha sort between those?

import os

from ament_index_python.packages import get_package_prefix
from ament_index_python.packages import get_package_share_directory
from launch import LaunchDescription
from launch.actions import ExecuteProcess
from launch_ros.actions import Node

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drake_ros_examples/examples/iiwa_manipulator/README.md line 40 at r1 (raw file):

Or
```sh
# Using ROS2 Launch

nit For consistency with others, can you put C++ first, Python second, and use the same comments?
e.g.

# Using ROS2 Launch (C++)
...
# or (Python)
...

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drake_ros_examples/examples/iiwa_manipulator/README.md line 40 at r1 (raw file):

Or
```sh
# Using ROS2 Launch

nit (here and elsewhere) Should use ROS 2 (with space), rather than ROS2 (no space)

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drake_ros_examples/examples/iiwa_manipulator/launch/iiwa_manipulator_py_launch.py line 18 at r1 (raw file):

    )

    # Node for multirobot in C++

nit copy-pasta, C++ -> Python.

Alternatively, consider removing these comments?

[adeeb10abbas]

Reviewable status: 4 of 12 files reviewed, 1 unresolved discussion (waiting on @EricCousineau-TRI)

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drake_ros_examples/examples/iiwa_manipulator/launch/iiwa_manipulator_py_launch.py line 18 at r1 (raw file):

Previously, EricCousineau-TRI (Eric Cousineau) wrote…

nit copy-pasta, C++ -> Python.

Alternatively, consider removing these comments?

yeah will just get rid of 'em! Done!

[EricCousineau-TRI]

Flake appears similar to #290 (most likely a timeout), merging for now (\cc @calderpg-tri @IanTheEngineer )