Add number of learners enrolled number to Pathway Dashboard

User Story

As an administrator or course team member, I want to see a current pathway enrollment numbers at the top of the Pathway Dashboard, so that I can quickly and easily monitor this enrollment snapshot and report out on it to leadership.

Acceptance Criteria

Description: An N Enrolled big number has been added to the Enrollment and Completion section of the Pathway Dasbhaord.
Given I am a user with access to the Pathway Dashboard
When I view the Enrollment and Completion section toward the top of the Pathway dashboard (under the Overview/Pathway Summary section)
Then I see an N Enrolled big number showing the count of learners currently enrolled in the currently filtered Pathway(s). This number should count a learner only once even if they are enrolled in more than one of the filtered pathways.
And I see that there is helper text on hover via a tooltip that indicates that: This number is the de-duplicated headcount number of currently-filtered pathway(s).

Start by locating the Pathway Dashboard's Enrollment and Completion section under the Overview/Pathway Summary section. Trace how the currently filtered pathways and learner enrollments are counted, then verify that learners enrolled in multiple filtered pathways appear once. Done means the N Enrolled number and hover tooltip show the de-duplicated current headcount.