feat(metric): bring feature parity between decorator and utility function

[flochaz]

Description of your changes

Bringing capture cold start metric and raise on empty metrics features to standard utility functions set.

How to verify this change

Now you can call captureColdStartMetric() and raiseOnEmptyMetrics() and get same behavior as of @metrics.logMetrics({captureColdStartMetric: true, raiseOnEmptyMetrics: true }) :

const metrics = new Metrics({ namespace: 'test' });

const handler = async (event: any, context: Context) => {
  metrics.captureColdStartMetric();
  metrics.raiseOnEmptyMetrics();
  // Logic goes here
  metrics.purgeStoredMetrics();
};

PR status

Is this ready for review?: YES
Is it a breaking change?: NO

Checklist

• My changes meet the tenets criteria
• I have performed a self-review of my own code
• I have commented my code where necessary, particularly in areas that should be flagged with a TODO, or hard-to-understand areas
• [] I have made corresponding changes to the documentation
• My changes generate no new warnings
• The code coverage hasn't decreased
• I have added tests that prove my change is effective and works
• New and existing unit tests pass locally and in Github Actions
• Any dependent changes have been merged and published in downstream module
• The PR title follows the conventional commit semantics

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[saragerion]

LGTM.
Shall we also add these in:

• examples folder
• mkdocs
  What do you think?

Either in this PR or in a next one

[flochaz]

LGTM. Shall we also add these in:

• examples folder
• mkdocs
  What do you think?

Either in this PR or in a next one

I have a PR updating mkdocs one will push the PR when this is merged. On examples, I plan a PR on refacto to make them more isolated and reusable so can include that