[11.x] Add doc for new helper method fluent() with more explaining

[lmottasin]

This PR adds documentation for the fluent() helper method, which is introduced in the framework #50848. The fluent() method is designed to simplify working with multi-dimensional arrays by providing intuitive methods.

Changes Made:

• Added documentation for the fluent() method with more explaining.
• Included usage examples demonstrating how to use fluent() for array manipulation
• Added a reference to the Fluent Class Documentation for further information on available options and methods

This documentation will help developers effectively understand and utilize the fluent() method for working with multi-dimensional arrays in their Laravel projects.

[lmottasin]

@PhiloNL Any suggestions?

[taylorotwell]

I really am not sure any of this needs to be documented. 😅 I know people keep trying to document it but it's a pretty obscure feature of the framework that was originally intended for internal framework use.

[michaloravec]

I'm pretty sure that this feature needs to be documented, in a few weeks no one will remember that the fluent helper even exists.