fix(exec): only pass script args to script

[Tobbe]

Let's say you run this command:
yarn rw exec normalScript positional1 --no-prisma positional2 --arg1=foo --arg2 bar -s

What Redwood will do is run your scrip named normalScript. It will also pass it the two positional arguments 'positional1' and 'positional2'. Plus the two named arguments arg1 and arg2 with the values 'foo' and 'bar' respectively. It will also read --no-prisma and skip generating a prisma client, and -s to run the script in silent mode.

What it would also do however is pass a bunch of extra stuff to the script, including the 'exec' word. This PR cleans all that up to only pass the actual script arguments to the script.

This is breaking because people might have been counting on those extra arguments to be passed to the script. Especially 'exec'because it gets passed to the script as part of the _ array. It was the first element, and (in this example) 'positional1' and 'positional2' would have come after it. So if people were expecting their first positional argument to be at args._[1] their script will now break.