accept an option for package name

[alexander-fenster]

We've got a weird problem when we started using pack-n-play. The generated system tests need to know the package name to require it properly, but the generator has no idea how the package is called.

E.g. for Text-to-speech, the actual name is @google-cloud/text-to-speech but we generate require('texttospeech') in system tests, and it fails.

For now, I solved this with a replace command in synth.py, but that's a hack. There are two possible options:

1. Make a generator flag to set the package name: gapic-generator-typescript ..... --package-name @google-cloud/text-to-speech

2. In pack-n-play, use some predefined name (e.g. library) for the library being tested, and write it to package.json manually, e.g. "library": "file.tgz" - that's what I did in my first system test (the one that is now removed).

I'm OK with both solutions (or any other possible solution you might have - let me know!), but I'd like to remove the synth.py hack as soon as possible :)

[alexander-fenster]

synth.py hack I was talking about: googleapis/nodejs-text-to-speech@abe65bf