Add SDK user facing code

[AndyTitu]

Summary

This MR introduces the developer facing code of the JS SDK. We are only aiming to support NodeJS for the beta.

Review Feedback Goals

• Gain enough confidence in the coding style used, and JS code patterns.
• Gain enough confidence in the UX - is the code in the examples folder user friendly? Would you like to use the SDK the way it's structured right now?
• Gain enough confidence in the tools being used - Jest for testing, ESModules etc.

How to test

Run tests with npm test or check the examples folder. For now please test via cloning this repo, as I didn't get the chance to publish this package to npm yet.

[AndyTitu]

For beta we are interested in supporting NodeJS, but how far away are we from supporting browsers as well, at this stage knowing that the Extism SDK that we'll use for interacting with the WASM core + the WASM core itself are browser compatible?

[jodyheavener]

While not absolutely critical, it might help for organization to have TS files like client, configuration, core, and secrets in a src or lib directory.

[AndyTitu]

While not absolutely critical, it might help for organization to have TS files like client, configuration, core, and secrets in a src or lib directory.

Done!

[armstrongl]

Some final notes:

• We'll want to decide early on how we'll talk about SDK actions like "allocation" and "deallocation."
• We should make sure we refer to the same things (or types of things) consistently.
  • It's not clear to me whether "WASM," "WASM core," and "SDK core" refer to the same thing in the context of the JavaScript SDK.
• Let's be explicit whenever possible. For example, instead of referring to "certain logic," let's identify the logic by what it is (e.g., a specific function).
• We should decide how we want to refer to the act of calling a function. In the Developer Portal, we usually use "call," but it might make sense to use "invoke" in this context due to the naming of the functions and interfaces (e.g., InvokeConfig).
• Even though this is an alpha release, I'd love to see a "quick and dirty" quick start guide telling the developer what to call and when.