[E2E][QIT] Migrate subscriptions e2e specs

[mgascam]

Fixes #WOOPMNT-5347

This PR builds on #11071.

It completes the migration of all WooCommerce Subscriptions E2E tests to the QIT framework and removes environment-based skip flags in favor of Playwright's native tag-based filtering system.

Changes proposed in this Pull Request

• Migrates 9 subscription specs (3 merchant + 6 shopper)
• Subscription products XML import setup
• Skip flag removal from all QIT specs
• goToActionScheduler utility function
• WooCommerce Subscriptions plugin integration in QIT bootstrap

Tag-Based Filtering

Removed environment-based skip flags from all QIT specs:

// ❌ REMOVED: Legacy skip pattern
const shouldRunSubscriptionsTests = process.env.SKIP_WC_SUBSCRIPTIONS_TESTS !== '1';
test.skip(!shouldRunSubscriptionsTests, 'Subscriptions tests are disabled');

Now using Playwright tags:

// ✅ NEW: Tag-based filtering
test.describe(
    'Subscriptions > Feature',
    { tag: ['@critical', '@subscriptions', '@merchant'] },
    () => { ... }
);

Benefits:

• Filter at runtime: npm run test:qit-e2e -- --tag=subscriptions
• Combine tags: --tag="critical & subscriptions"
• No inline skip logic
• Aligns with Playwright best practices

Testing instructions

# Run all subscription tests
npm run test:qit-e2e -- tests/qit/e2e/specs/subscriptions/

# Run specific test groups
npm run test:qit-e2e -- --tag=@subscriptions
npm run test:qit-e2e -- --tag="@critical & @subscriptions"

---

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• Covered with tests (or have a good reason not to test in description ☝️)
• Tested on mobile (or does not apply)

Post merge

• Link to testing instructions from release testing doc following these instructions : Add link here / 'QA Testing Not Applicable'
• Add or update critical flows and testing instructions for critical flows, if applicable.
• Add what's changed (description, screenshot, demo videos etc.) to the release announcement post, if applicable.