README formating and incorrect artifact coordinates

[timothystone-knsl]

The README referenced the old Maven coordinate for the AWS KMS. Update to the new coordinate and add some additional best practices in Maven such as the use of versions in properties. In code fences, add a syntax hint.

Unify the use of YAML mappings over "property" style keys, c.f., spring.cloud.aws. Where keys used camelCase, correct and use kebab-case for Spring recognition. Apply inline code style where needed, e.g., {cipher}. Use a single form of the YAML file extension, c.f., "yml" vs. "yaml".