feat: Queryset can now be filtered when populating index.

[qcoumes]

The idea of this MR is to allow filtering the queryset when populating the index.

Note that this only work by filtering models (with --models) which have the same column.

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filter and exclude arguments have been added to the methods DocType.get_queryset and DocType.get_indexing_queryset(). They take a Django Q object (both default to None) and are applied to the queryset.

Similarly, parameters --filter and --exclude have been added to the search_index command.

These parameters take a list of filter in the form <lookup>=<value>. Almost all django lookups are supported, including one chaining another (e.g. date_column__year__gt) and lookup spanning relationship (e.g.manufacturer__name).

The value can either be None (nullable_column=) an int (integer_column=2), a float (float_column=2.1), a datetime (datetime_column=2020-12-20T12:34+02:00) or a list of the previous types (integer_column=2,3,4). If none of the types above matched, the value will be interpreted as a string.

BREAKING CHANGE: Indices which overrode get_indexing_queryset or get_queryset need to define the filter=None and exlude=None arguments.