Add outcomes/activities to design phase

Why is this change being made?

Related to issue: #9065 (closed)

This MR is a first iteration of applying the activities/outcomes template to Validation: Design phase. The MR does the following:

1. Adds an overview for the phase to clarify goals and collaborators
2. Removes the step by step instructions and introduces a table of recommended activities and desired outcomes

Note: the intention is not to remove the "step by step" completely. We'd like to take the current steps in the pd-flow and link to them as part of a 'sample flow on a different page.

Author Checklist

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• Added a description to this MR explaining the reasons for the proposed change, per [say-why-not-just-what][transparency]
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