[FEATURE] React SDK: Provide hook to set relevant context "`useContextMutator`"

[toddbaert]

Background

The OpenFeatureProvider React context provider binds an OpenFeature client to a React Context. Components within that boundary use the associated client for evaluations, etc. The client can be associated with a domain (see https://github.com/open-feature/js-sdk/blob/main/packages/react/README.md#multiple-providers-and-domains and https://github.com/open-feature/js-sdk/blob/main/packages/client/README.md#domains)

We do not currently have a hook that makes it easy to update this context. It's necessary to use the global object to do this. We should add a hook that allows the correct context for the enclosed scope to be set.

For example, this current implementation:

<OpenFeatureProvider domain={'my-domain'}>
  <button
    onClick={() => {
      OpenFeature.setContext('my-domain', updatedContext);
    }}
  >
      click here
  </button>
</OpenFeatureProvider>

Could be instead be:

<OpenFeatureProvider domain={'my-domain'}>
  <button
    onClick={() => {
      mutateContext(updatedContext); // function returned by new hook, associated with the 'my-domain' domain
    }}
  >
      click here
  </button>
</OpenFeatureProvider>

This would make things easier for users, and fit better into react idioms. Please test your solution but using it in the sample react app here.

Requirements

• new hook added which returns function to mutate context (please come up with a reasonable name for the hook and returned function)
• associated tests
• associated README updates
• React demo updated here
• returned func(s) should probably be async

Additional Considerations

I'd love to see considerations from the implementor on the following:

• should we export a couple different functions? setContext, mergeContext etc, which merge the context?
• should we ignore changes if the reference hasn't changed?

[wichopy]

volunteer to tackle this one

[wichopy]

@toddbaert is there tooling to pull in the build with my changes in js sdk and use it with react test app project?

I was able to locally test manually using yalc but was wondering how you would go about it.

[beeme1mr]

Yalc is probably the easier way to try this in the test app.