Gimbal protocol v2 plugin - addressing PR comments

[Crowdedlight]

Addressing the PR comments from #1825 to help get the work done by Mark-Beaty merged in.

Copied in his PR description here:

This plugin has been tested with ROS2 Foxy and Humble and everything appears to be working correctly. Certain services and topics haven't been observed as working due to limitations of my testing hardware (Freefly Astro) and software (Auterion Simulator), but everything follows the documentation currently available for MAVLink's Gimbal Protocol v2. I also plan on adding another branch on my fork with the plugin separate from Mavros to enable use as a standalone plugin prior to the PR being approved/incorporated in a release.