Base architecture

[abnegate]

What does this PR do?

• Add base Adapter class
• Add base adapters for Email, SMS and Push
• Add adapters for Mailgun, Twilio and FCM
• Add mock adapters for Email and SMS (FCM could use request catcher, but investigating something more thorough)
• Add tests for Email, SMS
• Composer support
• Docker support
• GitHub workflows

[eldadfux]

A few suggestions:

• I would add all adapters under an Adapters folder
• All categories of adapters could still be at this path fore example: src/Utopia/Messaging/Adapters/Email/Mailgun.php
• With the new directory structure, specific abstract don't need a postfix. For example: EmailAdapter.php can just be Email.php
• Messages could be an independent directory alongside Adapters so each entity is independent. No need for a Message postfix we can leverage namespaces for that with the new dir structure.
• We should prefer shorter naming conventions when possible. sendMessage() can be just send()

[eldadfux]

Great work Jake! Left a few comments

[eldadfux]

We will probably hit HTTP request size limit before that.

[abnegate]

In that case the exception will propagate to the caller, the service has no limit, unless we want to apply an arbitrary one ourselves instead?

[eldadfux]

Not sure what might be the best approach, but we would need to take payload size to consideration at some point, either here or in Appwrite itself.