[4.2][Feature] Custom save request stripping

[tabacitu]

Fixes #3792
Depends on #3986 (that one needs to be merged into 4.2 first)

WHY

BEFORE - What was wrong? What was happening before this PR?

As reported in #3792 , if a dev wanted to strip the request in a different way than what saveAllInputsExcept allowed, it was difficult, they'd probably have to override the store() and update methods.

We were basically providing three options for saveAllInputsExcept:

• false or null => save ONLY inputs that have fields onpage
• ['one_item', 'another_item'] => save all input EXCEPT the ones in this array

This was very limiting.

AFTER - What is happening after this PR?

Instead of defining an array, you can define a closure where you do whatever you want to the $request and return an array of inputs you want saved.

HOW

How did you achieve that, in technical terms?

I've

• renamed the config from saveAllInputsExcept to strippedRequest
• changed it to allow null, true or closure

Is it a breaking change or non-breaking change?

Fo shizzle my nizzle.

How can we test the before & after?

Can't really test the "before", as it was working, but had limited capacity.

To test the "after" you can:

• define smth like this in your config/backpack/operations/create.php:

    /**
     * Before saving the entry, how would you like the request to be stripped?
     * - false - fall back to Backpack's default (ONLY save inputs that have fields)
     * - closure - process your own request (example removes all inputs that begin with underscode)
     *
     * @param  \Illuminate\Http\Request  $request
     * @return  array
     */
    'strippedRequest' => (function ($request) {
        return $request->except('_token', '_method', '_http_referrer', '_current_tab', '_save_action');
    }),

• do a dd($crud->getStrippedRequest()) in CreateOperation.php::store(), right before the call to $this->crud->create() (line 77).

---

This is ready to test & review. But before merging it:

• make sure you've merged Move operation configs to separate files #3986 (for @tabacitu )
• update the 4.2 docs - docs for changing saveAllInputsExcept to strippedRequest docs#287 (for @tabacitu )

[pxpm]

Nothing to say here.

Flawless job @tabacitu !