feat(client): Expose waitTask in the client

[julienbourdeau]

Q	A
Bug fix?	no
New feature?	yes
BC breaks?	no
Need Doc update	yes (not sure)

What was changed

2 methods about taskID initially available in the Index moved to the Client. The original methods on the index still work are not deprecated.

// New 🎉
$client->waitTask($indexName, $taskID, $timeBeforeRetry = 100, $requestHeaders = array())
$client->getTaskStatus($indexName, $taskID, $requestHeaders = array())

// Still available
$index->waitTask($taskID, $timeBeforeRetry = 100, $requestHeaders = array())
$index->getTaskStatus($taskID, $requestHeaders = array())

NOTE: The $timeBeforeRetry parameter is kept even if it doesn't exist in other clients. I believe it's a powerful feature.

Why it was changed

You could get some taskID from the engine without necessarily having an instance of Index. Instead of instantiating an index that you won't need, you can now call waitTask and getTaskStatus on the client.

• It will be very useful for the new Analytics object (see Introducing AB Testing #408)
• We're planning to merge Add multiple objects method to Client #295 (and port it to all clients). Adding multipleObjects will be easier to use if waitTask lives in the Client.
• It was also discussed before for the Django integration (here).