Further improvements of group imports history API

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This is issue for furthre improvements of group imports history API

• ATM, backend for retrieving bulk imports history provides items in chronological order - first item is oldest latest import. ~~This is counter-intuitive to user expectations, so we need either flip an order (simplest solution) or add backend parameter for controlling order~~

• Filtering by source groups is missing
• Author name is missing from API
• Original import host is missing from API response, so we're unable to render link to original group on remote instance - source_type is available in migration details endpoint.