chore: Python codegen runs in polymorph_code_gen and clean targets

[lucasmcdonald3]

Issue #, if available:

Description of changes:

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[texastony]

@lucasmcdonald3 If you have the time, it would be great to also add Python to the clean recipe.
For example, right now, when ever I need to re-polymorph the MPL, I run:

gmake clean;
rm -rf runtimes/python/src/aws_cryptographic_material_providers/smithygenerated

It should be straightforward to add the rm -rf of the Python Smithy generated to the Makefile.

[lucasmcdonald3]

Putting this PR on ice until Go gets merged.

This would create hiccups for Go that, ideally, we'd avoid for now.