Add rationale to SharePoint Baseline

[Sloane4]

💡 Summary

The new baseline structure is missing rationale for policy items.

Motivation and context

The rationale gives the user the importance of the policy item.

Implementation notes

Please provide details for implementation, such as:

• ADD Rationale section and text for each policy
  Note: Suggested format for Rationale
  • 1st sentence: Security risk if policy is not implemented.
  • 2nd sentence: How this policy minimizes this risk.

Acceptance criteria

How do we know when this work is done?

• All policy items have rationale sentences in place of TODO

[schrolla]

Waiting for other substantive changes in PR #360 to be merged prior to making rationale updates.

[schrolla]

Closed by merge of associated PR #393