feat(notifications): add title field to template data

[piksel]

This adds the field Title to the notification template data, so that it can be used inside the notification templates for services that doesn't normally have a way of displaying the title.
Note: This is only supported using the new templates (--notification-report)

Fixes #1052 (the second part) and fixes #1170.

[codecov]

Codecov Report

Merging #1125 (0e52235) into main (1d59fb8) will increase coverage by 0.26%.
The diff coverage is 91.66%.

@@            Coverage Diff             @@
##             main    #1125      +/-   ##
==========================================
+ Coverage   62.02%   62.28%   +0.26%     
==========================================
  Files          23       23              
  Lines        1480     1485       +5     
==========================================
+ Hits          918      925       +7     
  Misses        476      476              
+ Partials       86       84       -2     

Impacted Files	Coverage Δ
pkg/notifications/email.go	90.69% <66.66%> (-0.22%)	⬇️
pkg/notifications/notifier.go	77.35% <91.66%> (+5.35%)	⬆️
pkg/notifications/gotify.go	66.66% <100.00%> (ø)
pkg/notifications/msteams.go	66.66% <100.00%> (ø)
pkg/notifications/shoutrrr.go	74.39% <100.00%> (+0.97%)	⬆️
pkg/notifications/slack.go	94.87% <100.00%> (ø)

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