Store URLs found in HTML `<a>` and `<form>` tags during scan of HTML files
when recording scan metadata.
HTML URL recording will be ON by default, but is a part of the
generate-metadata-json feature.
The generate-metadata-json feature is OFF by default.
This introduces a new general scan option:
- libclamav: `CL_SCAN_GENERAL_STORE_HTML_URLS`.
- ClamD: `JsonStoreHTMLUrls`.
- ClamScan: `--json-store-html-urls`
Thank you Matt Jolly for the helpful comment on the pull request.