feat(repeat-members): a filter to replicate non-ensembles fields into ensemble fields

[floriankrb]

This seems to give good results with:

input:
  join:
    - mars:
        class: ea
        stream: enda
        type: an
        expver: "0001"
        number: 1/2/3
        grid: 20./20.
        param:
          - 2d
          - 2t
        levtype: sfc
    - pipe:
        - mars:
            class: ea
            type: an
            stream: oper
            expver: "0001"
            grid: 20./20.
            levtype: sfc
            param:
              - sdor
              - slor
        - repeat-members:
            numbers: [1, 2, 3]