Move form configuration tumors out of variant_values

[danr]

It would make more sense to return this in an own field in the configuration (tumors):

https://github.com/NBISweden/encam/blob/feature/backend-init/api/server.py#L89

While we're at it we can change from this old:

interface Conf {
  variant_values: {
    column: string,
    values: string[],
  }[],
  tumor_specific_values: {
    column: string,
    tumor: string,
    values: string[],
  }[],
  cell_types_full: string[],
  cell_types: string[]
}

to this new:

interface Conf {
  variant_values: {
    column: string,
    values: string[],
  }[],
  tumor_specific_values: {
    column: string,
    tumor: string,
    values: string[],
  }[],
  tumors: string[],
  cells: string[], // No point in sending cell_types_full
}

Making an issue because this will need a sync between backend and frontend