Implement run_script for pxp-agent

Users can currently run_task over pxp, but for run_script, they must first install the bolt_shim module, which converts any run_script actions to tasks so that pxp-agent can handle them.

Update pxp-agent so that it can run_script natively, the way it can already run_task.

Use methods from upload_file and run_command to implement run_script. run_script should be a single atomic operation from a protocol perspective.

run_script should look very similar to run_task. run_script should:

• Download the file to the cache dir
• Run the script from the cache dir with any arguments passed through the protocol.
• Replicate the windows specific "interpreter finding" logic
• Ensure run_script is "Purgeable" in the same way that run_task is
• the schema should look similar to run task with an additional array of "arguments" for the script to be run