[Feature] Add support for OSCAL format

[Boojapho]

🚀 Feature Proposal

I'd like to see the ability to import/export OSCAL formatted controls and assessments in CSET. More information can be found here: https://pages.nist.gov/OSCAL/ and https://csrc.nist.gov/Projects/open-security-controls-assessment-language

Motivation

NIST 800-53 will be released in OSCAL format. OSCAL is gaining adoption in the industry and government for standardized controls and assessments.

Example

By providing controls and assessments in OSCAL format, users can import/export to other tools for automation of control checks.

Pitch

Why does this feature belong in CSET?

With OSCAL gaining adoption in the industry and government, CSET can adopt the standard for controls/assessments to make interoperability easier. Use cases include automation, consolidating assessments, and quick import of standards.