Add Check Point security advisories importer

[NucleiAv]

Adds an importer for Check Point security advisories from https://advisories.checkpoint.com/advisories/, as listed in #2220 and #106.

The page has no official API. I generated an RSS feed via rss.app (https://rss.app/feeds/F22yOateJqF3fTZE.xml) to explore that path, but decided against using it for three reasons: it only captures recent entries with no historical data, severity is missing from the feed entirely, and it introduces a dependency on a third-party scraper that we don't control. The RSS feed items only have title (CPAI ID), description (summary text), link, and pubDate, etc. No severity field at all. The actual Check Point website has severity in two places, the listing table (Medium/High/Critical in column 0) and the individual advisory detail pages. The scraper gets it from the listing table itself. The rss.app feed just doesn't expose it. Scraping the source directly is the right call.

The importer paginates through all available years (detected from the year navigation links, with the current year always added since it does not appear in the nav). Each row in the advisory table maps as follows: the CPAI reference goes into advisory_id, the CVE ID goes into aliases and gets an NVD reference, and severity from the listing table goes into severities. Affected packages are not listed on this page so affected_packages is empty.