Split web_test_repositories() into per-language workspace rules.

[pcj]

To remove the rules_go dependency for a java-only project, consider splitting web_test_repositories() into java_webtesting_repositories() and go_webtesting_repositories(), loaded and called independently by the end-user.

[DrMarcII]

Web Test Launcher (the binary that actually manages all the servers required for web tests, and launches the actual test) is implemented in Go, so splitting the repositories rules would not remove the dep on rules_go.

[pcj]

Thx, clarified.