Allow disabling the auto group_concat behaviour on list column select properties for multi relations

[LukeTowers]

In https://github.com/octobercms/october/blob/develop/modules/backend/widgets/Lists.php#L502-L504 the select property of a column that references a relation with multiple associated record is automatically wrapped in a group_concat() call to automatically concatenate all of the results of the select query into a comma separated string.

This is fine behaviour by default, but a problem arises when attempting to use a DB engine that doesn't support group_concat (i.e. Postgres or SQL Server) or when attempting to do more complex select queries, such as summing a column on all the related records.

A new property, selectAutoConcat(open to suggestions for better names) should so that the current behaviour can be disabled by the developer when they want to handle those more advanced use cases.

[Rike-cz]

@LukeTowers What about sorting inside group_concat? #5424

[LukeTowers]

Hmm, I would probably say that once this is implemented #5424 would become unnecessary since you could just write out that SQL yourself. Seems like it might be a bit too magical to implement #5424. @bennothommo any thoughts?

[Rike-cz]

If you think using ORDER inside GROUP_CONCAT(), it's standard I think. But @bennothommo can have different opinion.

[daftspunk]

For complex scenarios like this, it should be handled by a custom column select using the list extension feature. It's basically the same thing and select acts as a defacto helper for this

[Rike-cz]

@daftspunk It could, but I think some ordering inside October's native group_concat feature is required. Now it shows items in random order.