Add Internal Customer DRI Responsibilities to Product Handbook

Why is this change being made?

We recently added the ability to define Internal Customer DRIs but not a definition of their responsibility. This adds a minimal version of that responsibility.

Closes - Product#804 (closed)

Does this MR meet the acceptance criteria?

Assign to DRI

• Did you assign this change to the correct DRI of the page or information you are changing?

Conformity

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