feat: emf multiple metric values

[to-mc]

Issue #, if available: #165

Description of changes:

Update metrics utility to support multiple values for the same metric name.

Checklist

• Meet tenets criteria
• Update tests
• Update docs
• PR title follows conventional commit semantics

Breaking change checklist

RFC issue #:

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

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[codecov-commenter]

Codecov Report

Merging #167 into develop will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop     #167   +/-   ##
========================================
  Coverage    99.79%   99.79%           
========================================
  Files           39       39           
  Lines          996      999    +3     
  Branches        83       83           
========================================
+ Hits           994      997    +3     
  Misses           1        1           
  Partials         1        1           

Impacted Files	Coverage Δ
aws_lambda_powertools/metrics/base.py	100.00% <100.00%> (ø)

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[heitorlessa]

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