[RHUI] rhui-manager cert upload command fails with "Error updating feed certificate on repo"

Issue

• Updating entitlement certificate on RHUA server using rhui-manager cert upload fails with following errors,

  [root@rhua ~]# rhui-manager cert upload --cert  export/entitlement_certificates/2189228412641827490.pem
  Updating repository rhel-7-server-ansible-2.9-rhui-rpms-x86_64 with certificate 2a9bf019cb414ef292b56b5f95c6c9af.pem...
  ... error during update, check the log for more information
  

• Following traceback logged in /root/.rhui/rhui.log after the execution of script /usr/bin/rhui-subscription-sync.

  2021-10-13 06:42:46,268 - Updating repository rhel-7-server-ansible-2.9-rhui-rpms-x86_64 with certificate /etc/pki/rhui/redhat/2a9bf019cb414ef292b56b5f95c6c9af.pem
  2021-10-13 06:42:46,283 - Error updating feed certificate on repo [rhel-7-server-ansible-2.9-rhui-rpms-x86_64]
  Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/rhui/tools/pulp_api.py", line 977, in update_content_cert
  self.repo_api.update(repo_id, {}, importer_config)
  File "/usr/lib/python2.7/site-packages/pulp/bindings/repository.py", line 119, in update
  return self.server.PUT(path, body)
  File "/usr/lib/python2.7/site-packages/pulp/bindings/server.py", line 104, in PUT
  log_request_body=log_request_body, ignore_prefix=ignore_prefix)
  File "/usr/lib/python2.7/site-packages/pulp/bindings/server.py", line 166, in _request
  self._handle_exceptions(response_code, response_body)
  File "/usr/lib/python2.7/site-packages/pulp/bindings/server.py", line 202, in _handle_exceptions
  raise exceptions.ApacheServerException(response_body)
  ApacheServerException