Backport to 2.8: Push upload responses return improper Content-Length header
CLOSED - CURRENTRELEASE
These responses: https://github.com/pulp/pulp_container/blob/master/pulp_container/app/registry_api.py#L145-L222 should set their
Content-Length header to 0 since they are not sending any data back in their body.
Fix improper Content-Length header in push responses
backports: #9516 closes #9521 (cherry picked from commit 29bd36bde33b0e4252efbe922d6e5a3555553a12)