Contribution to enhance OperationTable

[Zsombor Venczel]

Dear Sage development team,

I created a PR: https://github.com/sagemath/sage/pull/40108

It is a simple addition of a parameter `closed` to OperationTable to be used together with the parameter `elements` to indicate whether the `elements` are closed under `operation`. Without the modification if they weren't closed an exception was raised, but I would find it useful to include those elements in the table as well that go out of the original set.

Can somebody take a look at it, if this feature could be useful at all, or the way I aproached it in the code is OK?

Best regards,

Zsombor