Add plain provider to demonstrate provider support system
- Created PlainProvider implementation in src/providers/plain/
- Generates simple plain text mbox and JSON output
- Accepts any non-empty vulnerability ID format
- Uses PLAIN_USER environment variable
- Added to provider factory with 'plain' as the provider name
- Includes unit tests for the provider
- Added PROVIDERS.md documentation explaining the provider system
- Updated CLI help to show available providers
Signed-off-by: Sasha Levin <sashal@kernel.org>
3 files changed
