Add tests for set_value action and add kwarg support

[marcoroth]

This pull request adds tests for the set_value action. It also adds kwarg support for the action, previously only this worked:

turbo_stream.set_value("#input", "Value")

Which returned:

<turbo-stream targets="#input" action="set_value" value="Value"></turbo-stream>

Now all variations are supported:

turbo_stream.set_value("#input", "Value")
turbo_stream.set_value("#input", value: "Value")
turbo_stream.set_value(targets: "#input", value: "Value")
turbo_stream.set_value(target: "input", value: "Value")