feat: DB v2 component

[mandryllo]

This PR is the first one in order to resolve #70 and it will represent just the DB v2 component.

Changes:

• Due to the issues when creating a db from existing snapshot and investigation around it we decided to switch to aws native provider for the rds db instance. This resulted in these changes:
  • dbName and username are now optional (when creating db from a snapshot we can't provide them)
  • allocatedStorage type is now string
  • skipFinalSnapshot is removed because aws native doesn't support it
  • We discussed supporting blue/green deployments, but aws native doesn't support it
• Other changes:
  • autoMinorVersionUpgrade is now configurable
  • Component receives the whole VPC object instead of individual VPC properties
  • Component can receive existing KMS key
  • Component can receive customParameterGroupArgs to create a custom parameter group to use (you still can provide an existing parameter group)