Update keras-io to include KerasHub

[divyashreepathihalli]

The PR contains the following changes

• Adds KerasHub symbols
• Adds in the docs for vision models that are added to kerasHub
• Keeps KerasCV and KerasNLP sections on keras.io API symbols and guides - will be removed post official launch
• Ports all of KerasNLP guides to use KerasHub
• All of KerasNLP examples have be updated to KerasHub

[fchollet]

Thanks for the PR! Can you look into the test failure?

3.709 FileNotFoundError: [Errno 2] No such file or directory: '/templates/guides/keras_nlp/upload.md'

[fchollet]

If any URLs are getting switched from kerasnlp to kerashub, we need to add redirects for them. Please add entries in the redirects/ directory.

[divyashreepathihalli]

The updates have been made to files in the redirects folder.

[divyashreepathihalli]

Thanks for the PR! Can you look into the test failure?

3.709 FileNotFoundError: [Errno 2] No such file or directory: '/templates/guides/keras_nlp/upload.md'

The test failure has been has been fixed

[fchollet]

LGTM, thank you!