feat: sync primitives, network initialization

[hacdias]

This "small" first iteration adds:

• Sync Primitives: barriers, publish, subscribe, sugar methods, etc.
• Network initialization.

[hacdias]

@jacobheun @nonsense so I finish a first iteration. Most likely something will break. Next week I will work on a ping pong example (with the docker:generic builder) and make sure everything I wrote is working. After that, I will implement the docker:node builder, add some jsdoc for some good autocompletion, as well as update the README.

One question: we will have to publish this eventually on npm. Should the package be @testground/sdk or testground-sdk?

I'm merging this right now. However, please check the PR and I will update/fix/reply to your comments later.

[jacobheun]

One question: we will have to publish this eventually on npm. Should the package be @testground/sdk or testground-sdk?

@hacdias I'd recommend just creating the testground org in npm and going with @testground/sdk, as the org setup makes it easier IMO to manage user access for publishing.