Feature/Option: SecretsManager

Dependencies:

* IAM
* KMS

```yml
# TODO(IamPolicyDeveloper): SecretsManager: Read / write secrets
- Effect: Allow
Action:
- secretsmanager:PutSecretValue
- secretsmanager:GetSecretValue
Resource:
- !Sub "arn:aws:secretsmanager:${AwsRegion}:${AWS::AccountId}:secret:${ServiceName}/${Stage}/*"
# TODO(IamPolicyAdmin): SecretsManager: Manage secrets
- Effect: Allow
Action:
- secretsmanager:DescribeSecret
- secretsmanager:List*
Resource:
# Have to wildcard listing...
# TODO: ... but could do conditions + tags to limit
# https://docs.aws.amazon.com/secretsmanager/latest/userguide/auth-and-access_identity-based-policies.html
- "*"
- Effect: Allow
Action:
- secretsmanager:CreateSecret
- secretsmanager:DeleteSecret
Resource:
- !Sub "arn:aws:secretsmanager:${AwsRegion}:${AWS::AccountId}:secret:${ServiceName}/${Stage}/*"
```