Feature: Added support of ModelLifeCycle construct in Model Registry

[yash-aws-tech]

Issue #, if available:

Description of changes:
Added support for staging construct in Model Registry to describe the model life cycle for a model package. More details about the feature in this public doc (https://docs.aws.amazon.com/sagemaker/latest/dg/model-registry-staging-construct.html)

Testing done:

Ran unit tests and added additional ones as well.
Ran additionally added integ tests.

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.