Initialize repository

[nikitawootten-nist]

User Story:

As a NIST developer maintaining this repository, I would like minimally viable tooling for testing, documentation, and security checks in order to minimize friction while the project evolves.

Goals:

• Initialize as a private repository
• Configure permissions for users/teams
• Set up OSCAL team GitHub issue/PR templates and related files
• Design decisions documentation format
• Readme and contributing document
• Actions configuration for:
  • Automated unit testing #2
  • Automated linting checks #3
  • Automated static code analysis checks #4

[nikitawootten-nist]

Note, #2 is not "complete" as in tests cannot be written until the completion of #13, but the action to test the repo has been made. Marking this as finished.