Support ignoring some files on upload

[fent]

Hi! I thought it would be a good feature to support ignoring some files and directories that are zipped up and uploaded. For example, node_modules or src directories that are no longer used by the extension after a build step.

[fregante]

At the moment you just need to put everything into a folder. This also helps you automatically keep all extraneous files out — do you really want to exclude allll your config files explicitly?

At most we could automatically exclude what appears in .gitignore

[fent]

Hmm, my workspace is a bit different. The folder is the repo. And one of the dependencies is something I'm working on that I have symlinked to my extension while I'm working on both. And that dependency has webpack and a bunch of other build stuff on it, which adds like 40mb.

I guess for now I can unlink it before I publish.