Add offsets to probe sampler with new unit test

[mbkuhn]

Summary

Similar to the PlaneSampler, this PR adds the offset capability to the ProbeSampler. Offsets are added to the entire cloud of points within a given file.

Pull request type

Please check the type of change introduced:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

Checklist

The following is included:

• new unit-test(s)
• new regression test(s)
• documentation for new capability

This PR was tested by running:

• the unit tests
  • on GPU
  • on CPU
• the regression tests
  • on GPU
  • on CPU

Additional background

requested to go with terrain capability, e.g. terrain-aligned sampling

[hgopalan]

Thank you for adding this capability. Will help us generate terrain following slices.