Documentation: Complete CRUD example

Suggestion: In the "Build Your First Application" section of the docs, offer a complete CRUD app. That would allow a user to copy the code and immediately get underway. As it is, it's only halfway there.

Good!
If someone tries to send a Pull Request for adding new sections,
I recommend starting with 4.4 branch, not develop branch, because the tutorial has been updated for 4.4.
See https://github.com/codeigniter4/CodeIgniter4/pull/7427

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