Django 3.2 database improvements

• Functional indexes are now supported — we need to check models thatare often queried using a database function (e.g. aggregates), and add functional indexes for those queries (but leave the index out if write performance is more critical than search performance!)
• Index.include and UniqueConstraint.include are now supported for creating covering indexes — we should check whether we have queries that can be turned into index-only scans that way
• FilteredRelation now supports nested relations (probably most important for Alsijil)
• QuerySet.alias can be used instead of QuerySet.annotate for aliases that are only needed for filtering (probably most interesting for Alsijil)
• Transforms in expressions — not sure