[conflict_resolver] Add Cohort filter and field

[victori444]

Brief summary of changes

Adds a 'Cohort' filter and field to both unresolved and resolved tabs of the conflict resolver

Testing instructions (if applicable)

In the Unresolved & Resolved tabs:

1. In the Selection filter, verify that the 'Cohort' filter exists and has the appropriate options in the dropdown
2. Check that the 'Cohort' field appears as a column
3. Select any option and check that only conflicts of that cohort appear

CCNA Override