Select Bounty Permissions

**User Story:**
As a funder
I want to have flexibility on my bounties permissions
So that i can keep it open to the public or reserve it for a certain person

**Acceptance Criteria**
**Form Initaition**
GIVEN i am creating a bounty
WHEN I havigate to the additional details step
THEN I will have two options of how i can permission my bounty:
- Permisionless
- Approval Required
AND permisionless should be selected by default
AND only one of these options should be able to be selected

**Permissions - Selecting "Approval Required:**
GIVEN i am creating a bounty
AND i am on the additional details step
WHEN I click the "Approval Required" permission option
THEN the following fields will appear
- Auto Approve - check box, deselected by default
- Reserve Bounty - check box, deselected by default
AND those fields should be visible as long as approval required is selected

**Permissions - Reserve bounty selected**
GIVEN i am creating a bounty
AND i am on the additional details step
AND I have selected "Approval Required" as the permission option
WHEN i click "Reserve Bounty"
THEN i should be able to search contributors to reserve the bounty for
AND i should only be able to select one person

**Product & Design Links:**
https://www.figma.com/file/8AFLrc4dx9xnMXUkWOAaAR/Existing-Bounties-Updates?node-id=33%3A1854

Start with the bounty creation flow's additional details step and review the linked Figma design for the intended permission controls. Done means permissionless is selected by default, approval-required reveals the two checkboxes, and reserve bounty supports searching for and selecting one contributor as specified.

Written by the indexing model from the issue text.