`list issues` is currently unusable: `category` required by API, no flag exposed

[saramaebee]

What

fossapi list issues today always fails:

$ fossapi list issues --json --count 1
Error: FOSSA API error: Validation error: Invalid option: expected one of
"licensing"|"vulnerability"|"quality" at "category"

The underlying /api/v2/issues endpoint requires a category query param,
but the CLI neither passes a default nor exposes a flag.

Proposed fix

Add a --category flag (required, or defaulting to licensing), and while
you're in there, add filters the v2 endpoint supports:

fossapi list issues --category licensing|vulnerability|quality
                    [--status active|ignored|all]
                    [--page N] [--count N]
                    [--json]