✅📝 Add Feature to DiscussionEmbed for Compatibility with SSO

[chrisjtang]

Description

• Update DiscussionEmbed props and prop checking to display SSO properties if passed in as part of the config.
• Add tests to DiscussionEmbed for SSO rendering.
• Update ReadMe with DiscussionEmbed example Component.

Motivation and Context

This PR resolves issues and ambiguity around the compatibility of the DiscussionEmbed component with SSO, which was most recently surfaced in this issue: #135. In previous mentions of SSO compatibility, there were a few changes that were made but no example test sites were ever provided to confirm the validity of the compatibility. Once this PR gets merged and the NPM package gets updated, we will put up a React SSO example that is the equivalent to the current Disqus SSO example here: https://disqus-sso-demo.glitch.me/.

How Has This Been Tested?

• Added tests to the DiscussionEmbed test suite to test rendering when passing in an SSO config.
• Tested locally with a mock SSO setup that is using the updated DiscussionEmbed component to display SSO in React (this is the same example mentioned above that will be made available in the near future).

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• All new and existing tests passed.

[Hovspian]

lgtm