chore: FIx Metrics - Add missing array to wrap metrics array

[hjgraca]

Please provide the issue number

Issue number: #662

Summary

Changes

Add missing array that wraps Dimensions array

Empty Dimensions

{
  "_aws": {
    "Timestamp": 1728503062129,
    "CloudWatchMetrics": [
      {
        "Namespace": "dotnet-powertools-test",
        "Metrics": [
          {
            "Name": "Metric Name",
            "Unit": "Count"
          }
        ],
        "Dimensions": [
          []
        ]
      }
    ]
  },
  "Metric Name": 1
}

Dimensions with values

{
  "_aws": {
    "Timestamp": 1728503151889,
    "CloudWatchMetrics": [
      {
        "Namespace": "ns",
        "Metrics": [
          {
            "Name": "ColdStart",
            "Unit": "Count"
          }
        ],
        "Dimensions": [
          [
            "FunctionName",
            "Service"
          ]
        ]
      }
    ]
  },
  "FunctionName": "My Function with context",
  "Service": "svc",
  "ColdStart": 1
}

User experience

Please share what the user experience looks like before and after this change

Checklist

Please leave checklist items unchecked if they do not apply to your change.

• Meets 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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[codecov]

Codecov Report

Attention: Patch coverage is 78.57143% with 6 lines in your changes missing coverage. Please review.

Project coverage is 73.51%. Comparing base (5f62f2c) to head (af14147).
Report is 47 commits behind head on develop.

Files with missing lines	Patch %	Lines
...aries/src/AWS.Lambda.Powertools.Metrics/Metrics.cs	77.77%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #666      +/-   ##
===========================================
+ Coverage    73.49%   73.51%   +0.02%     
===========================================
  Files          203      203              
  Lines         8190     8206      +16     
  Branches       879      880       +1     
===========================================
+ Hits          6019     6033      +14     
- Misses        1880     1882       +2     
  Partials       291      291              

Flag	Coverage Δ
unittests	73.51% <78.57%> (+0.02%)	⬆️

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[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

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

See analysis details on SonarCloud

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
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