Bug: Metrics namespace and service should always be set

[hjgraca]

Expected Behaviour

Namespace and Service should always be set/checked to guarantee that the values are set manually or through env variables

Current Behaviour

If we did not set manually service and namespace would skip env variable check

Code snippet

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Possible Solution

No response

Steps to Reproduce

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Powertools for AWS Lambda (.NET) version

Metrics v2

AWS Lambda function runtime

dotnet8

Debugging logs