Improve docs search by customizing settings and page ranks

[mowies]

Goal

As a Keptn user, I want to use the search bar on the docs page to easily find the content that I am looking for in the version that I am looking for.

Details

Currently, we are using the local search on the docs page, this could be changed either to Algolia or a Google custom search with (presumably) much more flexibility in configuration compared to the local search.

DoD

• do research on the best search engine for the docs page and implement it
• de-rank pages from older versions

Notes

Some if not most of this issue will need to be done in the https://github.com/keptn/docs-tooling repo.