E2E: Add validation for canary environment

What does this MR do and why?

For context: gitlab-org/release/tasks#7124 (comment 1632760840)

When QA_COOKIES has gitlab_canary=true value, ensure that:

1. The browser as the cookie value set.
2. 'Next' badge is shown on the UI (in the sidebar menu next to GitLab Logo as shown in the screenshot below)

The validation is commented out in this MR (and enabled later) to ensure the data-testid="canary-badge-link" reaches both canary and main before we can start using it. This is a precaution we are taking to avoid any deployment blockers similar to what we experienced here: gitlab-org/release/tasks#7124 (closed)

Update:

Validation was enabled here: !136029 (merged)

Screenshots or screen recordings

How to set up and validate locally

1. Fire up the GDK
2. Comment the v-if="sidebarData.gitlab_com_and_canary" line here.
3. Uncomment the validate_canary! method call here.
4. Run any e2e against the gdk: QA_COOKIES="gitlab_canary=true" QA_DEBUG=true CHROME_HEADLESS=false bundle exec bin/qa Test::Instance::All http://gdk.test:3000 qa/specs/features/browser_ui/10_govern/login/log_in_spec.rb
5. To see the validation failing, run the test with v-if="sidebarData.gitlab_com_and_canary" mentioned in step 2 commented.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.