[automodel] add support for layer-freezing

[akoumpa]

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What does this PR do ?

Adds a callback to implement Dynamic Layer Freezing previously available in NeMo 1.0.

Collection: [Note which collection this PR will affect]

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Usage

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# Add a code snippet demonstrating how to use this 

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Additional Information

• Related to # (issue)

[chtruong814]

@akoumpa That test failure should be unrelated. We're going to make it optional. Please get a review, and I can merge this for you.

[HuiyingLi]

LGTM