[5.6] Add ability to override default api endpoint

[Miguel-Serejo]

Fixes #23864 by allowing a user to set a "mail.endpoints.sparkpost" config key to choose between available endpoints found at https://developers.sparkpost.com/api/

example addition to config/mail.php:

/*
|--------------------------------------------------------------------------
| Mail Service Endpoints
|--------------------------------------------------------------------------
|
| When using an email service, you might need to override the default API
| endpoints. This allows you to configure different endpoints based on your
| environment.
|
*/
'endpoints' => [
  'sparkpost' =>  env('SPARKPOST_ENDPOINT', 'https://api.sparkpost.com/api/v1'),
],

I'm not sure how to test this, but I would argue that any test to this feature would just be a test of the config helper.

I'm also unsure if other mail drivers should get the same treatment as I don't use any of them. It's an easy enough change to add to all the drivers for this PR if that makes sense at all.

It's a fairly simple change, and would only be a BC break if someone was using "mail.endpoints.*" already in their configuration. At a guess I would say that's unlikely, but if an argument is made for it we could easily change the config key at this stage.

[tillkruss]

This should be services.sparkpost.endpoint.

[GrahamCampbell]

You can't just call the foundation config function from the mail component. It doesn't exist.

[nunomaduro]

What @GrahamCampbell means is: The helper config() is not available if you use the package illuminate/mail individually.

[GrahamCampbell]

You can't just call the foundation config function from the mail component. It doesn't exist.

[Miguel-Serejo]

Thank you for the feedback.

Changed the implementation to fetch the endpoint from the options array. This requires adding the options array with the endpoint element to the services.sparkpost configuration as such:

'sparkpost' => [
        'secret' => env('SPARKPOST_SECRET'),
	'options' => [
		'endpoint' => env('SPARKPOST_ENDPOINT', 'https://api.sparkpost.com/api/v1');
	]
],

This is the minimal change I could find to avoid using the config helper. No changes to method signatures or constructor parameters. Could also be extended to other Transports if necessary.

One thing that I couldn't decide on was if setOptions should now also change the endpoint if it is present in the passed array or if explicit getter/setter should be declared. On one hand, I hesitate to change the public API mid-release, on the other hand, explicit setters would make it easier for devs to change only the endpoint. Could use some more opinions on this.

[taylorotwell]

Your constructor doesn't make sense to me. What if endpoint isn't in the options?

[Miguel-Serejo]

You're absolutely right. I'll give this another shot later today.