Use handle_outgoing_message for ZMQ replies

[Zsailer]

Follow-up on #1047.

This was an oversight in that PR. We should use handle_outgoing_message to reply on the websocket.

[blink1073]

Thanks!

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 77.85%. Comparing base (5646bf8) to head (0fa1fed).
Report is 279 commits behind head on main.

Files	Patch %	Lines
...ter_server/services/kernels/connection/channels.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1089      +/-   ##
==========================================
+ Coverage   77.47%   77.85%   +0.37%     
==========================================
  Files          68       68              
  Lines        8299     8299              
  Branches     1649     1649              
==========================================
+ Hits         6430     6461      +31     
+ Misses       1450     1438      -12     
+ Partials      419      400      -19     

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