Druid has previously refused to execute joins with non-equality-based
conditions. This was well-intentioned: the idea was to push people to
write their queries in a different, hopefully more performant way.

But as we're moving towards fuller SQL support, it makes more sense to
allow these conditions to go through with the best plan we can come up
with: a cross join followed by a filter. In some cases this will allow
the query to run, and people will be happy with that. In other cases,
it will run into resource limits during execution. But we should at
least give the query a chance.

This patch also updates the documentation to explain how people can
tell whether their queries are being planned this way.

Co-authored-by: Benedict Jin <asdf2014@apache.org>