apply aggregation support about odata-query

[OliverHofkens]

Hey @meitham,

There are currently no active plans to support $apply.
But I think it's a really cool use case, and would love to have it in the future (just like $select, see #1 ).

This is going to be a big change though, maybe even needing a seperate parser for each function. I'm not familiar enough with that part of the OData spec yet. Will have to look into it!

I think if we're going to go for such a big change, we might need to re-think the parser entirely. It's currently built with SLY, which seems to be retiring.

[troughton-carhartt]

Kind of crazy there isn't a really widely used Django OData library yet. This one could definitely fill that void - love it so far. Support for $top $skip $select $orderby at least would be huge. Hopefully can get some time to help out myself!