Add tests for Hydrodynamics plugin

[chapulina]

The plugin was added in #749 without tests. Since then, we've forked the plugin upstream in https://github.com/osrf/lrauv/blob/main/lrauv_ignition_plugins/src/HydrodynamicsPlugin.hh and made tweaks to fix bugs in the code. We should eventually port those fixes here and add tests verifying that the plugin behaves as expected.

Desired behavior

A new integration test that tests various aspects of the hydrodynamics plugin.

Implementation suggestion

The test should verify the hydrodynamics in isolation, so we're sure we're testing the effects of that plugin. Some ideas on how to do that:

• Set gravity to zero so we don't need buoyancy or a ground plane (that's similar to the Thruster tests added in Thruster plugin: add tests and velocity control #1190 )
• Apply forces / velocities directly to the vehicle without using extra plugins
• Measure the theoretical resulting velocities and accelerations based on the provided parameters

Additional context

• This may be useful for Port USV plugins from gazebo #1247

[arjo129]

For further information purposes and future reference the following lecture notes provide the necessary steps for computing added mass of simple shapes

• http://web.mit.edu/2.016/www/handouts/Added_Mass_Derivation_050916.pdf
• https://ocw.mit.edu/courses/mechanical-engineering/2-016-hydrodynamics-13-012-fall-2005/readings/2005reading6.pdf