[9.0] Add subscription state scopes

[timacdonald]

I've been using these in my applications and I had someone else ask about them, so I thought I would PR them and see if they might be handy having in the base package.

You can now apply query scopes based on the state of the subscription.

On trial

$users = User::whereHas('subscriptions', function ($query) {
    $query->whereName('gold')->onTrial();
})->get();

Active

$users = User::whereHas('subscriptions', function ($query) {
    $query->whereName('gold')->active();
})->get();

Cancelled

$users = User::whereHas('subscriptions', function ($query) {
    $query->whereName('gold')->cancelled();
})->get();

On grace period

$users = User::whereHas('subscriptions', function ($query) {
    $query->whereName('gold')->onGracePeriod();
})->get();

Ended

$users = User::whereHas('subscriptions', function ($query) {
    $query->whereName('gold')->ended();
})->get();

Recurring

$users = User::whereHas('subscriptions', function ($query) {
    $query->whereName('gold')->recurring();
})->get();

There are a couple of other added scopes, but they are just there to let these 👆ones work nicely under the hood.

These can come in handy when you want to email all your subscribers that perhaps have cancelled - or send a thank you for all your recurring subscribers once a year, etc.

// These users signed up and didn't even finish the trial before they cancelled.
// We might wanna reach out and see if they had any issues with the service.

$users = User::whereHas('subscriptions', function ($query) {
    $query->whereName('gold')->onTrial()->cancelled();
})->get();

As pointed out on Twitter this would also be handy for reporting.

Changes were done.

[taylorotwell]

Pretty cool, thanks.