add disable_product_check argument to transport classes

[OriHoch]

This PR adds the option to disable the product check for users who wish to do that (whether for performance reasons or if they are willing to take the risk of using an unsupported product)

It adds a disable_product_check argument to the transport class (sync and async)

The change is minimal, utilizing the existing _verified_elasticsearch variable and adding an additional False state to it which means that product check is disabled. Because the _ProductChecker.check_product method returns an integer, this new state does not interfere with the existing product check (if not disabled)

Tests were updated accordingly.

[elasticmachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?

[sethmlarson]

I've already closed an issue that requested this feature, it won't be implemented at this time.

[OriHoch]

thanks, would be good to have an explanation as to why.. it was already implemented here, so I guess not much additional work is needed to add it

[sftim]

Similar to #1675