Allow passing extra command-line flags to cargo

[RReverser]

💡 Feature description

I'm often building my packages on CI with --locked / --frozen after the dependencies have been downloaded.

I'd like to do the same with wasm-pack but currently there is no way to pass extra args to underlying cargo command.

💻 Basic example

I think it would make sense to be able to pass extra arbitrary args after -- as many other wrappers do, so that one could run:

$ wasm-pack build wasm-folder -- --frozen

[ibaryshnikov]

I would like to use it too

[ashleygwilliams]

i'm amenable to this for sure and once i get 0.6.0 out the door we can plan this for the next release!

[ashleygwilliams]

thanks to an unforeseen issue with the release last night which gave us some time to think on design, we'll be able to get this into 0.6.0.