Clarify what happens with repeating `Metric`s in `metric_config_bounds`

[llucax]

What's needed?

ElectricalComponent has a:

  // List of rated bounds present for the component identified by Metric.
  repeated MetricConfigBounds metric_config_bounds = 9;

Where:

// MetricConfigBounds describes a set of limits for a specific metric consisting
// of a lower and upper bound for said metric.
//
// This can be used for example to specify an allowed range of power output
// for a component.
message MetricConfigBounds {
  // Metric type the config bounds are for
  frequenz.api.common.v1alpha8.metrics.Metric metric = 1;

  // The set of bounds for the specified metric.
  //
  // This contains the lower and upper bounds for said metric.
  // Sources these may be derived from include the component configuration,
  // manufacturers limits, and limits of other devices.
  frequenz.api.common.v1alpha8.metrics.Bounds config_bounds = 2;
}

We need to specify what does it mean if there is more than one entry for the same Metric.

Proposed solution

It probably makes sense to aggregate all bounds ranges as a union, like we do with samples. This is what we are doing in client-common for now.

Use cases

No response

Alternatives and workarounds

No response

Additional context

No response