[Response Ops] Unskip 6 alert flyout tests in Scout spec

Implements tests 1-6 from alert_create_flyout.spec.ts that were
previously skipped due to missing Slack#xyztest preconfigured connector
and unavailable test.always-firing rule type.

Substitutions:
- Slack#xyztest → Slack connector created via API in beforeAll
- defineIndexThresholdAlert → Scout Playwright helper (tests 1-4)
- test.always-firing → .es-query rule type (tests 5-6)

Tests 11 (APM rule type) and 13 (filterBar.addDslFilter) remain
skipped as no Scout equivalent exists for those dependencies.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: guskovaue