DOCS-37 - New threat intel source

[jpipkin1]

Purpose of this pull request

This pull request adds a release note about the new default threat intelligence source. It also:

• Adds a new section to this article: https://help.sumologic.com/docs/security/threat-intelligence/about-threat-intelligence/
• Updates query examples in app articles.

Select the type of change

• Minor Changes - Typos, formatting, slight revisions
• Update Content - Revisions, updating sections
• New Content - New features, sections, pages, tutorials
• Site and Tools - .clabot, version updates, maintenance, dependencies, new packages for the site (Docusaurus, Gatsby, React, etc.)

Ticket (if applicable)

DOCS-37