Introduce absent data, particularly using data-absent-reason in FHIR exports

[eedrummer]

Requested Feature

Synthea should add features to remove data from output and supply a data-absent-reason.

Potential use cases:

• Creating faux anonymized data sets by omitting things like first and last names but supplying a data absent reason of masked
• Simulating errors in the system
• Simulating patient refusal to answer questions
• Simulating patients not knowing the answer to questions