Aws-secret-cdk

Include MD files.

Update to 1.60.0 and add upper dependency bound of 2.0.0.

Force update to CDK 1.44.0.

Restructure project having in mind that different types of rotations are
possible e.g. DynamoDB secret rotation, or RDS multi user secret rotation.
Narrowed down the permissions required for rotation. With this version
an aws-secret-cdk package is fully functional and available to be used.

Do not enforce KMS CMKs. Use assets to deploy lambda function source code
instead of S3 buckets. Use better prefixes. Refactor lambda function source code
to support initial passwords on existing databases. Warning: loosened permissions.
Next commit should fix them.

Update README.