Endpoint to Download Schemas Templates

[Buwujiu]

Create an endpoint that generates schema templates as a zip file with tsv templates.
Similar to this: https://clinical.platform.icgc-argo.org/api-docs/#/Dictionary/get_dictionary_template_all
The endpoint should generate zip file based on:

• dictionary name, version
  The zip file should include all schemas defined in the dictionary, all fields of each entity/schema, so users can use them as template to submit clinical data.

[Buwujiu]

Jon is working on Lectern refactor, let's wait until that is done.