[Docs] Add the ability to search through the docs

[aivinog1]

Describe the feature

Right now, the documentation does not have a search engine. It is very inconvenient to use it when you need to find information about specific checks, settings, etc.

Examples

You can see a good (IMO) example here: https://docs.camunda.io/. The search is on the main page, it has dropdowns with the most matched results while I am typing, article names where it found, etc.