Document the DISABLE_QUARANTINE variable

What does this MR do and why?

Add the DISABLE_QUARANTINE variable to the E2E documentation

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

How to set up and validate locally

Find a spec that is quarantined

Run eg.

DISABLE_QUARANTINE=true WEBDRIVER_HEADLESS=false bundle exec bin/qa Test::Instance::All http://gdk.test:3000/ ./qa/specs/features/ee/browser_ui/13_secure/enable_scanning_from_configuration_spec.rb

added QA maintenancerefactor typemaintenance labels

assigned to @willmeek

requested review from @adamcohen and @jay_mccure

added Quality label

added docs-only label

added development guidelines docsimprovement documentation labels

	1 Warning
⚠️	This merge request does not refer to an existing milestone.

	1 Message
📖	This MR contains docs in the /doc/development directory, but any Maintainer can merge. You do not need tech writer review.

If needed, you can retry the 🔁 danger-review job that generated this comment.

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approved this merge request

Thanks for creating this MR so quickly @willmeek! LGTM

requested review from @GitLabDuo

I finished my review and found nothing to comment on. Nice work! 🎉

approved this merge request

resolved all threads

started a merge train

changed milestone to %17.9

merged

mentioned in commit f6bb5eaa

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