Delays initialization on React

[ekwoka]

Solves a portion of #21

This PR:

• Refactors how the main widget package handles multiple calls to init using a store promise, allowing multiple calls to init to load only one instance while still having both "succeed" safely
• Provides prop and makes adjustments to React context provider to allow delaying of the initialization with context value passthrough (or init overrides)

I couldn't get tests to work at all locally (not entirely sure the steps needed to even run them as the readme seemed incomplete) so those will need to be checked, and possibly additional tests added for this.

[Shard]

Hi @ekwoka,

Sorry for the delay on getting this PR moving. I remember reviewing and testing the e2e locally earlier, then trying to get the e2e working for external contributors and getting distracted by life (as always 😄 ).

I'm just going to merge it into develop now and make sure its working fine before I look to cut a new release for this 🎉

Cheers again for the contribution 🥇