HSEARCH-1726 Allow performance validation tests to run on MariaDB


 - https://hibernate.atlassian.net/browse/HSEARCH-1726

Also reformatting the examples in the readme, as it's otherwise very unpractical to use.
OOI, why are you using in this example hikari as well, whereas you don't do it in the postgres case? I am actually going to close this pull request and create one of my own. I changed some formatting and wording.