Pass composite capabilities via CLI

[OndraM]

Currently only key:walue capabilities could be passed via CLI argument. More composite capabilities could be done using custom capabilities resolver. But the overhead seems to be a bit large for usecases like starting headless browser #233 etc.

So we may think about a format to pass even composite capabilities (like chromeOptions = { args = ['--headless']}} via CLI.

[rbrisita]

@OndraM Any update on this or the project in general? Currently using your library which helped immensely to test a legacy project and applied the CustomCapabilitiesResolver work around. Thank you for that!