[RFC] Remove LogGroupName as default dimension

This issue is to receive feedback on whether or not users want `LogGroup` as a default dimensions on your metrics. This was originally intended to enable deep-linking from metrics to the EMF events, but we no longer believe this is the correct approach to creating this linkage. This is a breaking change, so we want to hear your feedback.

https://github.com/awslabs/aws-embedded-metrics-node/blob/2ec8a84b7cc6081ff368aff501101a710367c6bb/src/logger/MetricsLogger.ts#L142-L147

Start by reading src/logger/MetricsLogger.ts at lines 142-147 and review the issue discussion for the requested feedback. This is an RFC for a breaking change rather than a defined implementation task; it is done only once the project reaches a decision about removing LogGroupName as a default dimension.

Written by the indexing model from the issue text.