Implement "application/zip" content type for "GET .../files" endpoint

[shiksha11]

Description

The TRS specification specifies that the GET /tools/{id}/versions/{version_id}/{type}/files endpoint may return, upon request (format parameter set to zip) a ZIP archive of all files, rather than the default response of a list of FileWrapper objects. This behavior was not yet implemented in #65.

Proposed solution

Resources outlining how to return the response as application/zip instead of application/json for the given endpoint are listed below:

• A ZIP archive of file contents (i.e., the values of FileWrapper.content for each file) needs to be created first, ideally in memory; in this ZIP archive, contents of individual file objects should be available as files with a relative path and filename that should, for each file, be taken from ToolFile.path (paths are relative to the PRIMARY_DESCRIPTOR file according to ToolFile.file_type)
• The ZIP file should then be sent to the client along the lines described here: https://stackoverflow.com/questions/27337013/how-to-send-zip-files-in-the-python-flask-framework; necessary changes to the codebase should likely happen here:

  trs-filer/trs_filer/ga4gh/trs/server.py

  Line 407 in 2158df4