[8.x] Model Broadcasting - Adding broadcastWith() and broadcastAs() support

[clemblanco]

This PR adds two optional model methods broadcastAs() and broadcastWith() when using Model Broadcasting.

---

When using broadcasting basic Events, we can specify which broadcast data and broadcast name should be used using both broadcastAs() and broadcastWith().

However, when using Model Broadcasting, we don't have that flexibility as it stands.

Similar to what the framework already does for broadcastOn(), we could use:

public function broadcastAs($event)
{
    return match($event) {
        'created' => 'server.created',
    };
}

public function broadcastWith($event)
{
    return match($event) {
        'created' => ['id' => $this->user->id],
    };
}

Just like broadcastOn():

1. not defining these methods will default to Laravel's default behaviour
2. not specifying a default within your match() statement will default to Laravel's default behaviour
3. if you'd like to always see the same broadcast data and/or name published, no matter the event, you could omit the match() expression (or switch() for php 7) and always return the same string or array

Bonus: missing unit tests

• The ability to use broadcastOn() to specify a channel for given events was not covered
• The default behaviours for the broadcast data and name were not covered

[driesvints]

Converted this to a draft until you've managed to fix the tests. Feel free to mark as ready when you're done.

[clemblanco]

@driesvints It's now ready even thought it seems like PHP 8.1 tests are marked as passed while it looks like GitHub Actions say otherwise.

Are you aware of this?

[driesvints]

@clemblanco yes, feel free to ignore those.

[clemblanco]

@driesvints In that case it's ready for you to have a look. Let me know what you think.✌️