Sendgrid-php: Add Rate Limiting Support

[thinkingserious]

We would like to add support for v3 Web API rate limits, as described here.

_How would you like this to be implemented?_ Or please give a thumbs up to express your interest in us implementing to move this task up our queue.

PRs are always welcome as well :)

[thinkingserious]

For reference, here is the implementation in our C# SDK.

[jopanel]

Hi,

Based on the C# implementation I think this would be an easy case.

// Reliability settings measured in seconds.
$reliabilitySettings = [
"retryCount" => 2,
"minBackOff" => 1,
"maxBackOff" => 10,
"deltaBackOff" => 3
];

$email->reliabilitySettings($reliabilitySettings);

I can make a PR but I would consider adding it to the refactor PR.

[thinkingserious]

Hi @jopanel,

If you have time, it would be nice to get it in now, while we wait for the refactor PR to be completed.

With Best Regards,

Elmer

[jopanel]

Hi

I hope I added it in the right place for this PR.

[thinkingserious]

Thanks @jopanel!

[mbernier]

@thinkingserious @jopanel I want to make sure I am following this properly, but is this issue closed by #439 ?