Support ZIP output

[fmigneault]

Description

When requested by Accept (and maybe f/format query?), a ZIP, TAR.GZ, etc. could be supported.
Resolution can be done the same way as the "multipart" branch in get_job_results_response, since all conditions leading to this result are similar (ZIP must be requested explicitly).

Given that ZIP or other similar containers would have to be requested explicitly, they do not necessarily need to be multi-value. They could contain a single file.

Tests

• Accept, f, format requesting ZIP (or others) returns them
• Single-output also returns it because requested explicitly
• Disambiguation of an output already producing ZIP (from the CWL)
  • does not cause nested ZIP for single value
  • (to consider) merges the contents for multi-value or should nest the ZIP?

References

• reference requirement: https://docs.ogc.org/DRAFTS/18-062.html#per_core_process-execute-multiple-output-pkg
• relates to Support Metalink as alternate multi-value output representation #663