fix(metrics): add warning for invalid dimension values; prevent their addition to EMF blobs

[leandrodamascena]

Issue number: #5526

Summary

Changes

Before this PR, if a customer added a dimension with an empty value, it caused EMF to skip all dimensions and create a metric without dimensions. For example:

{
    "_aws": {
        "Timestamp": 1731078543804,
        "CloudWatchMetrics": [
            {
                "Namespace": "kindle-scribe-llm-lambda",
                "Dimensions": [
                    [
                        "environment",
                        "stage"
                    ]
                ],
                "Metrics": [
                    {
                        "Name": "TEST_METRIC",
                        "Unit": "Count"
                    }
                ]
            }
        ]
    },
    "environment": "",
    "stage": "1",
    "TEST_METRIC": [
        1
    ]
}

This pull request enhances the metrics dimension handling by adding a warning for invalid dimension values and preventing these invalid dimensions from being added to the EMF (Enhanced Metric Format) blobs emitted by the utility.

Changes

• Implement a validation check for dimension values when adding a dimension to metrics
• Add a UserWarning warning to alert when an invalid dimension value is encountered
• Prevent dimensions with invalid values (empty strings or None) from being added to EMF blobs

User experience

Customer will get the following warning:

aws_lambda_powertools/metrics/metrics.py:117: UserWarning: The dimension **some_dimension** doesn't meet the requirements and won't be added. Ensure the dimension name and value are non empty strings
    self.provider.add_dimension(name=name, value=value)

Checklist

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• Meet tenets criteria
• I have performed a self-review of this change
• Changes have been tested
• Changes are documented
• PR title follows conventional commit semantics

Is this a breaking change?

RFC issue number:

Checklist:

• Migration process documented
• Implement warnings (if it can live side by side)

Acknowledgment

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Disclaimer: We value your time and bandwidth. As such, any pull requests created on non-triaged issues might not be successful.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.16%. Comparing base (3b2148e) to head (846d1f2).
Report is 3 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #5542   +/-   ##
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  Coverage    96.16%   96.16%           
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  Files          229      229           
  Lines        10812    10815    +3     
  Branches      2008     2009    +1     
========================================
+ Hits         10397    10400    +3     
  Misses         327      327           
  Partials        88       88           

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[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud