Add e2e-cli for E2E testing

[MichaelGHSeg]

Summary

• Adds e2e-cli/ — a standalone PHP CLI that reads a JSON event sequence via --input, sends events through the real Segment\Client, and outputs {"success": true/false, "sentBatches": N} to stdout
• Supports all six event types: track, identify, page, screen, alias, group
• Introduces E2eLibCurl subclass to inject http:// protocol for the mock test server (the base LibCurl hardcodes https:// with no option to override)
• Adds .github/workflows/e2e-tests.yml and publish-e2e-cli.yml
• Restricts e2e-config.json to basic test suite

Test plan

• php e2e-cli/main.php --input '{"writeKey":"...","apiHost":"...","sequences":[...]}' exits 0 and prints JSON
• Basic E2E suite passes: cd sdk-e2e-tests && CLI_COMMAND="php .../main.php" E2E_TEST_SUITES=basic npx vitest run
• e2e-tests.yml workflow runs clean on CI