docs: fastfit tutorial

[sdiazlor]

Description

Due to the problems with main, I prefer to recreate the PR in a clean branch. Here the notebook has been updated with the latest comments from the previous PR

Closes #4878

Type of change

(Remember to title the PR according to the type of change)

• Documentation update

How Has This Been Tested

(Please describe the tests that you ran to verify your changes.)

• sphinx-autobuild (read Developer Documentation for more details)

Checklist

• I added relevant documentation
• I followed the style guidelines of this project
• I did a self-review of my code
• I made corresponding changes to the documentation
• My changes generate no new warnings
• I filled out the contributor form (see text above)
• I have added relevant notes to the CHANGELOG.md file (See https://keepachangelog.com/)

[sdiazlor]

@davidberenstein1957 I recreated the PR from a clean branch just in case. Here all the comments are applied. Even if for the new SDK, we plan more simple, straightforward tutorials, I believe we can still add this to the old docs and create some content in the meantime.

[davidberenstein1957]

I agree. Thanks for the follow-up.