fix(gotify): handle token ending in /

[piksel]

This fixes a problem in gotify service, where it would not correctly handle a URL with only a token, but ending in /.
It also provides the full error messages as returned by the server upon failure.

[codecov]

Codecov Report

Merging #235 (8976d5b) into main (3261fbf) will increase coverage by 0.85%.
The diff coverage is 95.23%.

@@            Coverage Diff             @@
##             main     #235      +/-   ##
==========================================
+ Coverage   76.85%   77.71%   +0.85%     
==========================================
  Files          95       96       +1     
  Lines        2826     2863      +37     
==========================================
+ Hits         2172     2225      +53     
+ Misses        474      468       -6     
+ Partials      180      170      -10     

Impacted Files	Coverage Δ
pkg/services/gotify/gotify_json.go	0.00% <0.00%> (ø)
pkg/services/gotify/gotify.go	85.71% <100.00%> (+8.79%)	⬆️
pkg/services/gotify/gotify_config.go	90.90% <100.00%> (+2.67%)	⬆️
pkg/util/jsonclient/jsonclient.go	71.11% <100.00%> (+0.65%)	⬆️
pkg/util/partition_message.go	90.00% <0.00%> (-5.46%)	⬇️
pkg/util/util.go	100.00% <0.00%> (ø)
pkg/services/slack/slack_json.go	100.00% <0.00%> (ø)
pkg/services/mattermost/mattermost_json.go	100.00% <0.00%> (ø)
pkg/services/discord/discord_json.go	92.59% <0.00%> (+0.92%)	⬆️
... and 4 more

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