Allow to register multiple metrics for one validation (yaml input)

[jm-cc]

Currently only one metric is associated with an executable in the Validation list.

An executable may generate more than one metric, it should be possible to register them on the right entry rather than creating fake entries.

today :

(...)
      Validations:
        - id: metric-1
          type: configuration_independent
          reference : 100
          tolerance: 0.03
          executable: actual_executable
        - id: "metric-2"
          reference: 88.3
          type: configuration_independent
          tolerance: 0.1
          executable: true # noop executable since the metric is generated with previous validation.

wanted :

(...)
      Validations:
        executable : actual_executable
        metrics : 
          - {id : metric-1, reference : 100, type : configuration_independent, tolerance: 0.03}
          - {id : metric-2, reference : 88,3, type : configuration_independent, tolerance: 0.01}

Previous syntax for validation with only one metric will still be valid.

TODO

• Implement
• Example in gcvb-examples
• Write documentation