fix(monitor): a more powerful hack for quirks of Uptime Kuma

[favonia]

Close #648.

[favonia]

@JvdMaat I'm not sure what caused the strange bug you reported. However, the generation of notification messages has been completely rewritten (to support shoutrrr) so hopefully the problem is gone now? This PR additionally trim the failure messages before applying the existing ugly hack, in case messages with only space or newline characters were ever generated and somehow they confused the Uptime Kuma server.

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 6 lines in your changes missing coverage. Please review.

Project coverage is 90.30%. Comparing base (fd56d30) to head (ecd4fbc).

Files	Patch %	Lines
cmd/ddns/ddns.go	0.00%	6 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #774   +/-   ##
=======================================
  Coverage   90.30%   90.30%           
=======================================
  Files          52       52           
  Lines        2155     2156    +1     
=======================================
+ Hits         1946     1947    +1     
  Misses        198      198           
  Partials       11       11           

Flag	Coverage Δ
unittests	90.30% <33.33%> (+<0.01%)	⬆️

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[favonia]

@JvdMaat after reviewing the code I think the hack in this PR is overkill. I'm reverting it to a simpler/cleaner one that is hopefully sufficient. 🕵️