Replace usage of dummy-pipeline with nextclade pipeline without alignment

[fhennig]

The dummy pipeline is a bit neglected, and not very resilient with incorrect data (crashes instead of giving an error). We want to instead use the nextclade pipeline without alignment. For this, the nextclade pipeline needs to support file sharing features.

Blocking: loculus-project/loculus#5942

In PPX there is the not-aligned-organism which uses the nextclade pipeline without alignment already. This is how prepro is configured there:

    preprocessing:
      - version: 4
        image: ghcr.io/loculus-project/preprocessing-nextclade
        args:
          - "prepro"
        configFile:
          log_level: DEBUG
          batch_size: 100
          segments:
            - name: main
              references:
              - name: singleReference
                genes: []