removed events_listener; added basic test for webhooks_listener

[bigcat88]

Starting with Nextcloud 30 there is a webhooks_listener app that is enabled by default and supports both regular requests and requests from ExApps!

It has much more and better functionality than events_listener in AppAPI, and we will remove events_listener for Nextcloud 32 from AppAPI.

In this PR I am removing events_listener and reworking the tests for events_listener into basic tests for webhooks_listener.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.13%. Comparing base (0965823) to head (06e4f59).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #348      +/-   ##
==========================================
+ Coverage   94.52%   95.13%   +0.61%     
==========================================
  Files          46       45       -1     
  Lines        5389     5325      -64     
==========================================
- Hits         5094     5066      -28     
+ Misses        295      259      -36     

Files with missing lines	Coverage Δ
nc_py_api/nextcloud.py	96.26% <ø> (-0.08%)	⬇️
nc_py_api/webhooks.py	94.84% <100.00%> (+40.40%)	⬆️

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