Draft PR: react-js template for wxp on Toolkit

[YueLi-MSFT]

Thank you for your pull request! Please provide the following information.

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Change Description:

Describe what the PR is about. 

1. Do these changes impact any npm scripts commands (in package.json)? (e.g., running 'npm run start')
   If Yes, briefly describe what is impacted.

2. Do these changes impact VS Code debugging options (launch.json)?
   If Yes, briefly describe what is impacted.

3. Do these changes impact template output? (e.g., add/remove file, update file location, update file contents)
   If Yes, briefly describe what is impacted.

4. Do these changes impact documentation? (e.g., a tutorial on https://docs.microsoft.com/en-us/office/dev/add-ins/overview/office-add-ins)
   If Yes, briefly describe what is impacted.

If you answered yes to any of these please do the following:
> Include 'Rick-Kirkham' in the review
> Make sure the README file is correct

Validation/testing performed:

Describe manual testing done. 

[millerds]

This repo needs to continue to support all host for xml and not be converted to just json for your specific scenario. There are changes being made to the repo to support both json and xml and you should wait and base your changes of that.

I would also note that when generating projects we currently have the user pick hosts to start with. If you want to change from that either to add the option for all hosts or to replace host specific options with always generating for all hosts then some more thought need to go into the design of the template with others (documentation team owns the content of the project and Outlook team should have a say) such that it's not overly complicated and easy enough to trim down when developers don't want everything.

[millerds]

We cannot merge changes into master that are not ready for production. (WXP support is not even in preview yet)