add testground (node + browser) test to this repo

[GlenDC]

Follow-up task from #26.

Now that sdk-js (this repo) is supposed to work both in the browser and nodeJS alike,
it would be good to have a testground testplan to ensure this continues to work.

@laurentsenta assigned it to me and we can find inspiration for this in the rust-sdk.

[GlenDC]

@laurentsenta in our next sync we can try to define the kind of tests that would be useful and desired, both for Node and Browser. If we can come up with an initial list of tests I can also start working on this in the background.

[laurentsenta]

@GlenDC that sounds great, thanks for taking over this task.

Some notes here to make sure every contributor has access to the discussion:

We'd get a huge confidence improvement by having "some tests now," the rust SDK suite is a good example here (we caught some bug with just these two tests): https://github.com/testground/sdk-rust/blob/master/examples/example.rs

If we add, on every PR:

• in node js only (because it requires almost no setup)
• a simple example that logs a message,
• a simple publish subscribe that uses the sync service,

That would be a great improvement,

The main problem we'll have to think about with browser tests is that they require a lot of code we'll have to move from the testground repo (maybe git clone the repo, maybe wait for native support in testground, maybe...)

[GlenDC]

Ok let's for now perhaps already start with just the NodeJS ones. Those plans can than be run in browser once we have official support for the browser.

Shall I start working on native support of browser in testground @laurentsenta ?