[Docs] Broken Links

[smokestacklightnin]

URL(s) with the issue:

Please provide a link to the documentation entry:
https://tensorflow.github.io/tfx/

Description of issue (what needs changing):

After merging PR #6914, there are still bona fide broken links. These are not technical issues with the documentation stack, but rather links from the authors of the docs that point to invalid locations or get 404 responses.

Here is a list generated by lychee:

Errors in docs/guide/tft_bestpractices.md

• [404] https://keras.io/guides/preprocessing_layers/ | Failed: Network error: Not Found

Errors in docs/guide/transform.md

• [ERR] https://developers.google.com/machine-learning/crash-course/embedding | Failed: Network error: error sending request for url (https://developers.google.com/machine-learning/crash-course/embedding)

Errors in docs/tutorials/transform/data_preprocessing_with_cloud.md

• [ERR] file:///home/william/google-tensorflow-ci-cd/tfx/docs/tutorials/transform/data-preprocessing-for-ml-with-tf-transform-pt1#preprocessing-operations | Failed: Cannot find file
• [404] https://www.tensorflow.org/products/calculator#id=fad408d8-dd68-45b8-954e-5a5619a5d148 | Failed: Network error: Not Found

Errors in docs/tutorials/tfx/airflow_workshop.md

• [ERR] file:///home/william/google-tensorflow-ci-cd/tfx/guide/beam_orchestrator | Failed: Cannot find file
• [404] https://airflow.apache.org/cli.html | Failed: Network error: Not Found

[lego0901]

Thanks for the investigation! I fixed the 4 missing links from #6918.