feat: implement SSM

[sam-goodwin]

Closes #5

With this one, learned about the API reference some times containing examples API requests including all the headers which is helpful: https://docs.aws.amazon.com/systems-manager/latest/APIReference/API_GetParameter.html

Also learned about the various content types for JSON which is annoying. I wonder how many permutations are required here:

const contentTypeMap: Partial<Record<keyof SDK, string>> = {
  DynamoDB: "application/x-amz-json-1.0",
  SSM: "application/x-amz-json-1.1",
};

Should look into generating these look up tables from a manifest, as suggested here: https://twitter.com/jenschude/status/1615373732926656518?s=20&t=FWEvbqlfpTbT0Cn0q8AvYA