Forward reference dataset and retrieve URL for input params

[ejseqera]

Re #116

Testing out functionality to retrieve the dataset URL referencing a dataset name using YAML anchor and provide URL as input param in params-file.

To test:

datasets:
  - name: &dataset 'test-sqkit-dataset'
    file-path: './examples/yaml/datasets/rnaseq_samples.csv'
    description: 'My test dataset'
    workspace: 'scidev/testing'
    overwrite: True
launch:
  - name: "nf-core-rnaseq"
    pipeline: "nf-core-rnaseq"
    workspace: 'scidev/testing'
    params:
      input: *dataset 

This YAML creates a dataset, where the name is used as an anchor and the alias is referenced in the params block. The utils.update_dataset_params() method will retrieve the appropriate URL for the dataset to be used when launching a pipeline, or adding it to the Launchpad.

TODO:

• Add docs on usage
• Add tests