Expand CISA BOD 26-04 page into actual howto & reference pages #1180

We moved pretty quick to get #1164 out the door, leaving us with docs/howto/cisa_response.md as a fairly thin, "mostly reference" page without much in the way of extra content.

This issue is a placeholder for future work to do one or both of the following:

• Expand the docs/howto/cisa_response.md page into an actual "how to" document
• Add a page in docs/reference that covers just the Decision Table reference material (Add CISA BOD 26-04 decision framework with Asset Exposure decision point #1164 already added reference pages for the decision points).

Additional context:
The second item above also implies the need for a docs/reference section about DecisionTable objects we have defined in the project. We do not currently have reference docs for any of these (they only appear in other "how to" pages, which is not really Diátaxis-friendly.