Add feeds file option for notification title prefixes

[VerifiedJoseph]

Adds feed file option for prepending text to notification titles.

- name: Example feed
  url: https://example.com/feed.rss
  interval: 600
  ntfy_topic: test
  title_prefix: Status change!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (f2849d3) to head (98543e7).
Report is 12 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##                main      #193   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
- Complexity       236       241    +5     
===========================================
  Files             25        25           
  Lines            576       589   +13     
===========================================
+ Hits             576       589   +13     

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