feat(metrics): adopted Utility class

[dreamorosi]

Description of your changes

This PR introduces changes to the Metrics module to adopt the forthcoming Utility class that will be released in the @aws-lambda-powertools/commons package.

• Install released @aws-lambda-powertools/commons package
• Make changes to the code to use the Utility class
• Run unit & e2e tests
• Add note in the docs about initialising utility outside of function handler (ref)

How to verify this change

See checks running on PR, see screenshot below for e2e tests ran locally:

Optionally re-run e2e on GitHub Action.

Related issues, RFCs

#484
#547

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
• 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

Breaking change checklist

N/A

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[dreamorosi]

This PR is on hold until #547 is merged & released.

[ijemmy]

LGTM