refactor: simplify bazel saucelabs targets using karma pre-test wrapper and shared saucelabs connection between tests (#34769)

* Added a /tools/saucelabs/sauce-service.sh script that manages the sauce-connect as a service which is used by the karma-saucelabs.js wrapper to start the service.
* Added /tools/saucelabs/README.md that covers the details of SauceLabs karma testing with Bazel.

PR Close #34769