[RF-DOCS] Active Record Callbacks (rails#51654)

Review and improve Action View Overview guide. [ci-skip]

* Samples that use Proc.new {} can likely be simplified to just use proc {}
* Link to the validations guide where we mention it under conditional callbacks
* after_find callbacks are also triggered by a few other methods: take, sole, find_by!
* We could potentially add some more examples on different types of callbacks that aren't there.
* Updated some sections for clarity

Co-authored-by: Petrik de Heus <[email protected]>
Co-authored-by: Carlos Antonio da Silva <[email protected]>
Co-authored-by: hatsu <[email protected]>

Author: 4 people