Add Tasks for Nightly QA Schedule to Security Patch Template

What does this MR do and why?

This MR proposes adding tasks to disable the Nightly QA schedule while Omnibus nightly builds are paused during a security release, notify the QA team and to enable again once the builds are enabled and an updated package is available.

This is to help inform QA about upcoming security releases and to reduce noise for QA on-call DRIs by preventing nightly tests from failing either against an outdated package or when mirroring is down.

Author Check-list

• Update https://about.gitlab.com/handbook/engineering/quality/quality-engineering/debugging-qa-test-failures/ after this MR has been merged