Add support for loading Config items from AWS Secrets Manager and Parameter Store

[adam-buckley]

Support is needed for loading Config items from Secrets Manager and possibly Parameter Store. Since Parameter Store uses SSM it may be simpler to just use Secrets Manager.

The connection to Secrets Manager should be done via the AWS PHP SDK (included in Cmfive), documentation on using the PHP SDK for Secrets Manager is here.

The pulled value must be a JSON encoded string, that the Config class then parses and merges into the base Config register. Isaac has started work on this, the branch is here: .

Semi related is: 2pisoftware/cmfive-boilerplate#154