Skip false positive dependency scanning advisories

Proposal

Our dependency scanning feature relies on the GitLab Advisory Database to match dependencies with known advisories. At times, we have yanked (changed decision on) advisories from the database because they have been disputed, and proven to be false positives. These advisories are titled as False postive in the database, so we have a heuristic where we can skip over the vulnerability creation if:

1. They're sourced from GLAD
2. They're titled False positive

This would prevent unnecessary vulnerability openings, and reduce the noise in the security reports of our customers.

Implementation

1. Update Gemnasium's advisory matching to skip vulnerabilities that have a False Positive Name.
   1. Create tests that verify the advisory is skipped during vulnerability creation.
2. Update the pm_advisories ingestion to skip ingestion and scanning of advisories that have a False Positive title and and have glad as the source_xid.
   1. Add test that verifies the advisory ingestion is skipped.
3. Update PMDB to skip ingestion of advisories that have a False Positive title and are sourced from glad
   1. Add unit test that verifies the advisory ingestion is skipped.