Docs: Align SECURITY.md with the jQuery organization security policy

[timmywil]

jquery-ui's SECURITY.md predates the organization template and has no escalation path, no list of what a report should contain, and no policy on automated reports. Because the repository has its own file, it does not inherit the organization-wide one from jquery/.github.

This replaces it with the same template now proposed for core in jquery/jquery#5925 and for the organization in jquery/.github#2, with jQuery UI specific wording.

• Supported Versions notes that jQuery UI supports multiple jQuery versions and that fixes are not backported.
• Reports must include the jQuery UI and jQuery versions tested, the specific API with file and line, a runnable proof of concept, and an own-words description.
• Adds the "Report quality and automated submissions" subsection and the OpenJS Foundation CNA escalation path.
• The contributions cross-reference points at the organization CONTRIBUTING.md, since this repository's own CONTRIBUTING.md does not have that section.