Add support for local dependencies in parent directory

[ohayon]

I am certainly no docker expert, but this is my understanding:

Because my file structure is as follows:

• Project
  • Xcode Project
  • Swift packages that are dependencies for the server and the app
  • server directory
    • All my server code and Package.swift

The current plugin is not able to find the dependencies once everything is in docker.

Adding a --parent flag allows the workspace to move up a level and properly build the server app.

Also the size of the output has been quite huge, last run before stripping it was something like 400mb (I also could definitely be doing something wrong here), so I added in some stripping to keep it under Vercel's 100mb limit. Should probably put that behind a flag too.

Open to any and all feedback or changes you'd like to see, but also open to you just saying I should keep this on my own fork.