fix(gotify): use pkr for fields to make them settable from url

[piksel]

This adds the title and priority fields to the config and URL (previously only settable with params).
It also adds support for disabling TLS for non-https servers.

Ref: containrrr/watchtower#761

[codecov]

Codecov Report

Merging #116 (3f2846b) into main (1290cec) will increase coverage by 2.61%.
The diff coverage is 78.94%.

@@            Coverage Diff             @@
##             main     #116      +/-   ##
==========================================
+ Coverage   52.79%   55.41%   +2.61%     
==========================================
  Files          55       55              
  Lines        1161     1164       +3     
==========================================
+ Hits          613      645      +32     
+ Misses        512      479      -33     
- Partials       36       40       +4     

Impacted Files	Coverage Δ
pkg/services/gotify/gotify_config.go	86.66% <75.00%> (+86.66%)	⬆️
pkg/services/gotify/gotify.go	73.33% <81.81%> (+44.76%)	⬆️

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