Create a policy template for writing AWS Systems Manager - Parameter Store parameters #1673

Description:

Currently, the only policy template available for AWS Systems Manager - Parameter Store is the SSMParameterReadPolicy 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.