add ignore_object_ids to snap_down API

[aclegg3]

Motivation and Context

This PR adds optional ignore_object_ids to the snap_down API. This allows particular objects to be ignored in the collision and raycasting checks.

A good example of utility is using snap_down to determine a placement location for an object on the floor. Ideally, the robot's own body would not be considered in the validation checks when locating a placement position. Those ids could be added to the ignore list.

How Has This Been Tested

Added a simple CI test.

Types of changes

• [Development] A pull request that add new features to the habitat-lab task and environment codebase. Development Pull Requests must be small (less that 500 lines of code change), have unit testing, very extensive documentation and examples. These are typically new tasks, environments, sensors, etc... The review process for these Pull Request is longer because these changes will be maintained by our core team of developers, so make sure your changes are easy to understand!

Checklist

• [x] My code follows the code style of this project.
• [x] I have updated the documentation if required.
• [x] I have read the CONTRIBUTING document.
• [x] I have completed my CLA (see CONTRIBUTING)
• [x] I have added tests to cover my changes if required.