[Feature] CatFrames constant padding

[albertbou92]

Description

Allows the CatFrames Transforms to use constant padding using any specified value, instead of only zeros.

Motivation and Context

Why is this change required? What problem does it solve?
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You can use the syntax close #15213 if this solves the issue #15213

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Types of changes

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds core functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (update in the documentation)
• Example (update in the folder of examples)

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• I have updated the documentation accordingly.

[vmoens]

Sounds reasonable but these changes are bc breaking. IMO we can live with both zeros and constant (zeros would be a shortcut to constant with 0 value). If you think it's best to keep only constant we should raise a depreciation warning.

[vmoens]

LGTM some minor suggestions