Remove allow_experimental_join_condition for Default Non-equi Conditions

Why it matters

This change simplifies the usage of non-equi join conditions by removing the need for an experimental flag. Users can now write more flexible join expressions without additional configuration, improving query expressiveness and ease of use.

How to use it

Non-equi join conditions are now available by default. Users can write join queries with arbitrary conditions without setting allow_experimental_join_condition.