Remove Slack bot token from e2e on-demand tests

[luhi-DT]

Description

Remove Slack bot token from e2e on-demand tests and replace it with the webhook URL

How can this be tested?

Run e2e on demand tests and check slack notification

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.38%. Comparing base (ca3d9b6) to head (adc98cc).
Report is 1 commits behind head on main.

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Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3898   +/-   ##
=======================================
  Coverage   64.38%   64.38%           
=======================================
  Files         372      372           
  Lines       20543    20543           
=======================================
  Hits        13227    13227           
  Misses       6034     6034           
  Partials     1282     1282           

Flag	Coverage Δ
unittests	64.38% <ø> (ø)

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