Extension:CirrusSearch/ES6CompatTransportWrapper

This Elastica transport class allows CirrusSearch to work with elasticsearch 6.8.23 while using ruflin/Elastica 7.1.5. It can be enabled like this:

This mainly allows writes to be properly applied. It was used on the WMF infrastucture to allow a zero-downtime upgrade migration plan. It is strongly advised to upgrade to elasticsearch 7.10.2 rather than using this compatibility layer.