Create a policy template for writing AWS Systems Manager - Parameter Store parameters

## Description:

Currently, the only policy template available for [AWS Systems Manager - Parameter Store][ssm-parameter-store] is the _[SSMParameterReadPolicy][ssm-parameter-read-policy]_ for reading parameters.

This means that users, especially those creating nested workflows, must handcraft AWS IAM policies to update parameters via AWS SAM applications.

I am submitting a PR separately which contains a proposed _SSMParameterWritePolicy_ template with the additional required permissions per the Systems Manager documentation.

[ssm-parameter-store]: https://aws.amazon.com/systems-manager/features/#Parameter_Store
[ssm-parameter-read-policy]: https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-policy-template-list.html#ssm-parameter-read-policy