3.19 - Refactor features to use rocket_head new approach

[wordpressfan]

Is your feature request related to a problem? Please describe.
We started a discussion here with @remyperona to have an approach to unify the addition of link tags inside head directly after the closing tag of title but without any duplication, and we proposed a solution here

So we need to move forward with this approach (we may need to unify the way we insert link into the head using a trait or functions, this will make it more maintainable)

So the main goals of this issue are:

1. Set the standard of the items being added into head, something like Priority 10 for link tags, priority 20 for styles, ...etc.
2. Create the trait to insert the items into head, so instead of using the following code:

add_filter( 'rocket_head_items', function ( $items ) {
    $items[] = [
        'open_tag' => '<link',
        'rel' => 'preload',
        'href' => 'https://example.org/',
        'close_tag' => '/>',
    ];
    return $items;
} );

we can use something like:

add_filter( 'rocket_head_items', function ( $items ) {
    $items[] = $this->add_preload_link( 'https://example.org/' );
    return $items;
} );

and do the same with other types of link types and styles.
3. Refactor the other features like RUCSS, critical CSS, and any other feature that add items into the head (you can search for the closing title tag into the code to reach all instances) and then make sure that the features are working properly.