[Task]: Modify agency filter to do exact matches rather than the strbegins approach we have

[chouinar]

Summary

After chatting with the front-end folks, they plan to send us every agency nested inside of an agency, so we don't need to keep the confusing agency prefix approach we have.

We can change the query from:

            stmt = stmt.where(
                or_(*[Opportunity.agency.istartswith(agency) for agency in one_of_agencies])
            )

to

            stmt = stmt.where(
                Opportunity.agency.in_(one_of_agencies)
            )

and fix tests accordingly

Acceptance criteria

• Logic adjusted as described above