[Feature] Update puppetfile/getDependencies

[glennsarti]

Use Case

PR 255 added the puppetfile/getDependencies

• Update the call to read in the document if it's not already in the cache (or perhaps transfer the entire file content)?
• Create a data contract for the response (What should the repsonse have in it)
• Should the response be a flat list of all modules or a tree based response
• Better error responses for the different types of errors