Filter bounty explorer by type

**User Story:**
As a contributor
I want to filter the bounty explorer by the new types
So that i have a good user experience and my filtering matches the updated types of bounties

**Acceptance Criteria**

GIVEN I am on the bounty explorer
WHEN I am trying to filter by bounty type
THEN I should see filters for the updated bounty types:
- Open to 1 worker (this would filter to show only traditional bounties)
- Open to multiple workers (this would filter to show only multiple bounties)

**Product & Design Links:**
https://www.figma.com/file/8AFLrc4dx9xnMXUkWOAaAR/Existing-Bounties-Updates?node-id=123%3A622