Remove ConfigSetup() during the Prometheus input plugin Start() method to fix configuration reset
Remove ConfigSetup() during the Prometheus input plugin Start() method to fix configuration reset

  During the startup process, the prometheus module is first configured using `prometheus.ConfigSetup()` and `prometheus.ConfigProcess()`, then the Handler is started. The problem is that `ConfigSetup()` is called from `Start()`, which makes the configuration re-initialize to its default values. Removing the call from `Start()` solve the issue.

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