Rename `import-profile` to `import-baseline`

[aj-stein-nist]

User Story:

As an OSCAL tool developer or security practitioner, in order to best understand what I can import in an OSCAL system security plan as a baseline, be it a profile or a fully resolved catalog, I would like the relevant attribute in a SSP to be more accurately named import-baseline or a sensible equivalent vetted and supported by the NIST team and community.

Goals:

The goal is to increase the clarity of intent and application with the import-profile directive to support either a profile or catalog, and the current name, even with documentation updates, will likely cause confusion.

This was discussed #1227 (comment) as the long-term solution.

Dependencies:

{Describe any previous issues or related work that must be completed to start or complete this issue.}

Acceptance Criteria

• Update SSP model to change from import-profile to import-baseline.
• All OSCAL website and readme documentation affected by the changes in this issue have been updated. Changes to the OSCAL website can be made in the docs/content directory of your branch.
• A Pull Request (PR) is submitted that fully addresses the goals of this User Story. This issue is referenced in the PR.
• The CI-CD build process runs without any reported errors on the PR. This can be confirmed by reviewing that all checks have passed in the PR.

{The items above are general acceptance criteria for all User Stories. Please describe anything else that must be completed for this issue to be considered resolved.}