Add language configuration support for DiscussionEmbed component

Description

Note: Depending on the completeness of the translation for a given language, and the release of language support from disqus, the strings displayed on discussion thread UI may not be completely translated.

Motivation and Context

This is an attempt to address the requirement raised on https://github.com/disqus/disqus-react/issues/12

How Has This Been Tested?

Tested with the Gatsby production web site on https://thefabulouslifestyles.com/

Screenshots (if appropriate):

Types of changes

~~- [ ] Bug fix (non-breaking change which fixes an issue)~~

[X] New feature (non-breaking change which adds functionality)

~~- [ ] Breaking change (fix or feature that would cause existing functionality to change)~~

Checklist:

[X] My code follows the code style of this project.
[X] My change requires a change to the documentation.
- [X] I have updated the documentation accordingly.

disqus / disqus-react

Add language configuration support for DiscussionEmbed component #66