Add validation to Job schedule to prevent scheduling jobs every second

[peterbppb]

Added validation to schedule to prevent jobs running every second as this breaks dkron and the nodes need to be restarted to clean up the hanging jobs.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.33%. Comparing base (21c9383) to head (2099ee3).
Report is 35 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #52      +/-   ##
===========================================
- Coverage    88.49%   81.33%   -7.16%     
===========================================
  Files           14       17       +3     
  Lines          513      627     +114     
===========================================
+ Hits           454      510      +56     
- Misses          59      117      +58     

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