fix(metrics): Rename leftover reference to purgeStoredMetrics() function

[ijemmy]

Description of your changes

Rename the term "purge" that was missed by the PR #377

This will solve issue #423

How to verify this change

cd examples/cdk
# switch to target aws account
cdk deploy 
aws lambda invoke --function-name <function_name_should_start_with_CdkAppStack-MyFunction>
# check that the EMF is published on CloudWatch log

Related issues, RFCs

#377
#423

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

Breaking change checklist

• I have documented the migration process
• I have added, implemented necessary warnings (if it can live side by side)

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[flochaz]

Will add examples testing as part of our CI/CD workflow