Refactored MetricsDefinition to use a MetricBuilder and be based off a super class

[lksfrnz]

Refactored the MetricDefinition to inherit a Metric super class which can be inherited by other type of metrics (coming soon). Also refactored MetricDefinition to be immutable and created a MetricDefinitionBuilder which behaves similar to how MetricDefinition used to.

Naming is also handled using a setter instead of on creation for simplicity in upcoming metric changes.

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[markkuhn]

If we want to build the feature first before merging into master, then this PR should point to a feature branch and not master.

[lksfrnz]

Tested f59577b on the example lambda and metrics were reported as expected.

This commit refactored the previous implementation to now follow the lombok Builder's format as suggested by @markkuhn. However, lombok's @Builder becomes very messy when dealing with inheritance which is why only its format was used here instead of the actual annotation.

[lksfrnz]

Tested c3fa3e8:

• The example lambda published metrics as expected
• All relevant unit tests passed

[gordonpn]

LGTM