Add support for scheduled messages

[stnguyen90]

What does this PR do?

Update the schedule worker to support messages

Test Plan

Manual

Related PRs and Issues

Checklist

• Have you read the Contributing Guidelines on issues?
• If the PR includes a change to an API's metadata (desc, label, params, etc.), does it also include updated API specs and example docs?

[stnguyen90]

getDocument() shouldn't have a filter query:

appwrite/src/Appwrite/Platform/Workers/Messaging.php

Line 148 in 6de2659

$provider = $dbForProject->getDocument('providers', $providerId, [Query::equal('enabled', [true])]);

[stnguyen90]

Wherever we check for providers, we need to check whether they're enabled. e.g.:

appwrite/src/Appwrite/Platform/Workers/Messaging.php

Line 126 in 6de2659

if (!$providerId && $primaryProvider instanceof Document && !$primaryProvider->isEmpty()) {

appwrite/src/Appwrite/Platform/Workers/Messaging.php

Line 150 in 6de2659

if ($provider->isEmpty()) {