Elastic 9 client support for 8.x?

[niemyjski]

Is your feature request related to a problem? Please describe.
How much of a drift is it really for Elastic 9 client to work with 8? Minus some api's not working? We are in a weird spot where we are on Elastic 8 running nest, had to target 9.x client due to 8.x doesn't contain all the fixes 9.x does (which supports elastic 9/10)

Describe the solution you'd like
A guide or reduced support for Elastic 8 during transition period?

Describe alternatives you've considered
Was going to run our full test suite against elastic 8 with 9 client.

[niemyjski]

From initial testing this feels like it's going to be a ton of work when the health check endpoint starts having issues. I'm going to work to see what can be done to downgrade to elastic 8 client and what all needs to be backported or work around...