AsyncInit only makes sense for regular lambda mode

[smirnoal]

Excerpt from
https://github.com/awslabs/aws-serverless-java-container/wiki/Quick-start---Spring-Boot2#asynchronous-initialization

However, AWS Lambda limits the initialization phase to 10 second

this is only true for regular invokes. Provisioned concurrency and SnapStart have different timeouts. Async Init doesn't make much sense for the SnapStart usecase in particular, so it would be good to keep this option for regular invokes only.