Disable CloudFormation support by default

[maciejwalkowiak]

CloudFormation is one of many ways to provision infrastructure on AWS. There are many reports from confused users who do not use CloudFormation and usually solution to their problem is turn disable ContextStackAutoConfiguration. To ease getting started experience and also make it simpler to use the framework for non-CloudFormation users cloud.aws.stack.auto should be false by default.

[eddumelendez]

this one can be address as part of #582

[eddumelendez]

following this comment #582 (comment) As far as I can see, we can deprecate spring-cloud-aws-context in 2.3.x and remove it 3.0.x.