Add a Feed form: ask for clarification when feed is not official

### Describe the problem

When a user selects "No" to "is this feed an official source", display two new optional fields: 

1. "Why was this feed created?" text box
2. "How often is this feed updated?" text box 

### Proposed solution

See above

### Alternatives you've considered

_No response_

### Additional context

_No response_