Add new strings to process docstrings

[sachinprasadhs]

Added Usage: Example usage: and Sample usage: to highlight in bold, which is having numerous entries in keras.io.

Example:
https://keras.io/api/keras_cv/layers/augmentation/random_augmentation_pipeline/
https://keras.io/api/keras_nlp/models/gemma/gemma_backbone/

[fchollet]

I'd rather we standardize the docstrings on either Examples: or Example: or Usage:.

[sachinprasadhs]

I'd rather we standardize the docstrings on either Examples: or Example: or Usage:.

Makes sense, shall I make the changes in the code or use the same logic to write something like
docstring = docstring.replace("Example usage:", "# Example\n")

[fchollet]

I would recommend converting all the titles containing "usage" to just "Example usage:"

[sachinprasadhs]

Closing this PR since it is no longer needed and all the usages and examples are converted to Example: or Examples:

keras-team/keras#19344
keras-team/keras-cv#2399
keras-team/keras-hub#1516