Stub: search click-through rate

[mxk0]

Summary

Ensuring we can measure:

Search accuracy: Set a baseline metric for accuracy, as measured by monthly click-through rate (CTR) for results on the first page.

#1892 may achieve this.

Acceptance criteria

• Tracking in place to measure conversion rate from "performs search" to "clicks on an opportunity listing link"

[mxk0]

Moving this into #1892 as an acceptance criterion