feat(test-runner-browserstack): Make the local proxy configurable

[fbuecklers]

What I did

1. I introduced a top level local options, which allow you to disable the local proxy setup. This is specially useful when you just want to test public reachable domains
2. I have made the internal IP lookup conditional based on the capability.local flag, to make sure that it will only be run in cases it is really needed. This is also useful in CI environments where the ip command may not be available. Even an import of the module has previously crashed such CI runs.

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: ec574b7f6c71560bfc9aa27a492ac32d601ef9f7

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@web/test-runner-browserstack	Minor

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[fbuecklers]

Hi @Westbrook Thanks for the quick review. I have hopefully addressed your points

[fbuecklers]

@Westbrook Does it look good for you now?