Update documentation

[yahia-kerim]

Checklist: #576.

• Update the documentation to explain the async/await syntax & the new options.
• Add a typescript example on how to setup the plugin.
• Add Mkdocs configuration file to generate a simple, beautiful static website for the documentation.
• Split the documentation into files (each file is corresponding to a page in the static site).
• Add the versioning to the generated static site to save the current v4.6 doc.
• Automate the static site generation using Github actions.

Using Mkdocs & Material for MkDocs theme, the generated static site will be pushed to a branch called gh-pages & deployed using Github pages.

Please check my forked repository yahiakr/mongoosastic:gh-pages for more details.

The generated static site is deployed here: https://yahiakr.github.io/mongoosastic/

[guumaster]

This is looking amazing already. Excellent work!