refactor: improve metric creation logic and silence ot warnings

[ogabrielluiz]

This pull request refactors the metric creation logic in the opentelemetry.py file and improves the handling methods for metrics. It enhances warnings and ensures that the key in the mapping and metric's name are the same. Additionally, it simplifies the metric creation process by using a helper method _create_metric().

[github-actions]

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_{Last Modified at 05 Aug 24 20:57 UTC}

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