How to categorize this PR?

/area documentation
/kind enhancement

What this PR does / why we need it:
Following is done in this PR:

1. Small corrections to docs
2. Introduced mkdocs specific configuration (YAML and CSS)
3. Added github action to publish the docs
4. Adapted docs to use mkdocs plugins

Which issue(s) this PR fixes:
Partially fixes #897

Special notes for your reviewer:
Once this PR is reviewed and merged there are some additional steps that needs to be done:

• Create an orphan and empty gh-pages branch. To create such a branch do the following:

git checkout --orhpan gh-pages
git rm -rf .
git commit --allow-empty -m "<commit-msg>"
git push origin gh-pages

• Configure github pages to use gh-pages branch

To view the docs you can see this in the fork https://unmarshall.github.io/etcd-druid/index.html

Release note:

Introduced github pages to host the etcd-druid documentation