feat: Add support for MetricDefinitions in ModelTrainer

[chad119]

Issue #, if available:
Issue: #5018

Description of changes:

• Adding support for MetricDefinitions following existing .with_xxx pattern
• Enable usage like below:

  from sagemaker.modules.train import ModelTrainer
  from sagemaker.modules.configs import MetricDefinition

  metric_definitions = [
      MetricDefinition(
          name="loss",
          regex="Loss: (.*?);",
      )
  ]

  model_trainer = ModelTrainer(
      ...
  ).with_metric_definitions(metric_definitions)

Testing done:

• Added unit tests and tested end to end for sanity

Merge Checklist

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General

• I have read the CONTRIBUTING doc
• I certify that the changes I am introducing will be backward compatible, and I have discussed concerns about this, if any, with the Python SDK team
• I used the commit message format described in CONTRIBUTING
• I have passed the region in to all S3 and STS clients that I've initialized as part of this change.
• I have updated any necessary documentation, including READMEs and API docs (if appropriate)

Tests

• I have added tests that prove my fix is effective or that my feature works (if appropriate)
• I have added unit and/or integration tests as appropriate to ensure backward compatibility of the changes
• I have checked that my tests are not configured for a specific region or account (if appropriate)
• I have used unique_name_from_base to create resource names in integ tests (if appropriate)
• If adding any dependency in requirements.txt files, I have spell checked and ensured they exist in PyPi

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.19%. Comparing base (70b2f9a) to head (7616328).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5202      +/-   ##
==========================================
+ Coverage   86.18%   86.19%   +0.01%     
==========================================
  Files         446      446              
  Lines       43267    43277      +10     
==========================================
+ Hits        37290    37304      +14     
+ Misses       5977     5973       -4     

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