Add Gotify priority environment variable

[VerifiedJoseph]

Adds environment variable VIGILANT_NOTIFICATION_GOTIFY_PRIORITY to control Gotify message priority.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (a6900fe) to head (11f25f8).

❗ Current head 11f25f8 differs from pull request most recent head 6251d92. Consider uploading reports for the commit 6251d92 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##                main      #159   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
- Complexity       211       214    +3     
===========================================
  Files             23        23           
  Lines            512       518    +6     
===========================================
+ Hits             512       518    +6     

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