Feat: optimise active dref query

[susilnem]

Changes

• Remove n+1 query
• Use annotate on active dref query
• Refactor serializer changes

Checklist

Things that should succeed before merging.

• Updated/ran unit tests
• Updated CHANGELOG.md

Release

If there is a version update, make sure to tag the repository with the latest version.

[szabozoltan69]

Thanks for this fix, dear @susilnem

[susilnem]

@szabozoltan69 , Can you check and verify this before merging?

Here's the output I got:

[szabozoltan69]

I checked the output before and after the change.
It's great.
There is some slight change, giving
final_report_details": null
when there is no final report, but that is fine.

The old one looked like:

      "final_report_details": {
        "title": "",
        "national_society": null,
        "disaster_type": null,
        "type_of_dref": null,
        "appeal_code": "",
        "country": null,
        "status": null,
        "date_of_approval": null
      },

   – the new is better.