[Docs] Add docs for custom entity with access per admin channel

[Tomanhez]

Q	A
Branch?	master
Bug fix?	no
New feature?	yes
BC breaks?	no
Deprecations?	no
License	MIT

[lchrusciel]

Good to have this document here, but we should think about making this process simpler

[lchrusciel]

Can we have this form type predefined in Plus and use it somewhere?

[Tomanhez]

Yep. I think we should replace all places with ChannelChoiceType for ChannelPerAdminChannelChoiceType. This is not scope this task, but good improvement in future. Next good improvement is to add resources name as parameters in services, without decorating ResourceChannelEnabilibityChecker service:
Now:

final class ResourceChannelEnabilibityChecker implements ResourceChannelEnabilibityCheckerInterface
{
    public function forResourceName(string $resourceName): bool
    {
        return in_array($resourceName, [
            'credit_memo',
            'customer',
            'invoice',
            'order',
            'payment',
            'product',
            'product_variant',
            'return_request',
            'shipment',
        ]);
    }
}

It could be more generic, for example:

final class ResourceChannelEnabilibityChecker implements ResourceChannelEnabilibityCheckerInterface
{
    private $resources;

    public function __construct($resources)
    {
        $this->resources = array_merge(
            $resources,
            [
                'credit_memo',
                'customer',
                'invoice',
                'order',
                'payment',
                'product',
                'product_variant',
                'return_request',
                'shipment',
            ]
        );
    }


    public function forResourceName(string $resourceName): bool
    {
        return in_array($resourceName, $this->resources);
    }

After this changes, final application needs overwrite only service and add new entity names

[GSadee]

We definitely should at least define in ResourceChannelChecker, in Plus the behaviour for checking the entity with ChannelAwareInterface and then recommend for implementing this interface instead of decorating this service

[GSadee]

The base of this pull-request was changed, you need fetch and reset your local branch
if you want to add new commits to this pull request. Reset before you pull, else commits
may become messed-up.

Unless you added new commits (to this branch) locally that you did not push yet,
execute git fetch origin && git reset "add-custom-entity-accessing-per-admin-channel" to update your local branch.

Feel free to ask for assistance when you get stuck 👍

Everything has been fixed

[GSadee]

Thank you, Tomasz! 🎉