[Feature]: Add IN Operator to PQL

[cancan101]

There is no IN operator defined in PQL: https://docs.pimcore.com/platform/Generic_Data_Index/Searching_For_Data_In_Index/Pimcore_Query_Language/.

It might just be syntactic sugar for a sequence of = EXPRESSION joined by OR, but it would still be useful for user ergonomics.

[github-actions]

Thanks a lot for reporting the issue. We did not consider the issue as "Pimcore:Priority", "Pimcore:ToDo" or "Pimcore:Backlog", so we're not going to work on that anytime soon. Please create a pull request to fix the issue if this is a bug report. We'll then review it as quickly as possible. If you're interested in contributing a feature, please contact us first here before creating a pull request. We'll then decide whether we'd accept it or not. Thanks for your understanding.