fix: Invalid key error for metric_filter and dimension_filter

[pedroceriotti]

This PR fixes the issue introduced by #186.

It was causing the tap to break if no metric filter or dimensions are defined in the reports.json, or if these keys are defined with camelCase notation, which would be reasonable given it's a JSON file and all the other dimension and metric values use camelCase notation.

The issue was that the keys were defined with camelCase on lines 113-114 on the client.py file when initializing the report_definition dictionary, but it then tries to access them using _snakecase notation on lines 267-268, which caused the tap to break with an invalid key error.

[sonarcloud[bot]]

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