[profilingtometrics]: remove metrics_prefix configuration option

[rogercoll]

• Renaming a metric is in the scope of a processor component. For example, the following configuration is equivalent to the metrics_prefix: "my.metrics" configuration option:

processors:
  transform:
    metric_statements:
     - context: metric
       statements:
         - replace_pattern(name, "(.+)", "my.metrics.$$1")

• Replaces the mockMetricsConsumer test structure in favor of collector's consumertest package

[rogercoll]

This is not needed atm, the actual ConsumeMetrics implementation cannot return an error.

[christos68k]

Is there automated formatting in this repository that's consistent and reflects these changes? I see make gofmt but that doesn't result in additional formatting changes.

To avoid confusion with inconsistent formatting (that also adds additional review load as extra lines of code need to be checked) I suggest we first update the automated formatting in this repository to reflect these changes so that we all have a way to keep formatting consistent. Otherwise, we'll keep running into formatting inconsistencies as we use different editors with different settings.

[rogercoll]

sounds good! I will create a follow-up PR for that. In any case, I removed the formatting changes for this PR f80e74d