Make poll interval configurable per source

[davidv1992]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 82.60870% with 64 lines in your changes missing coverage. Please review.

Project coverage is 81.53%. Comparing base (ef33a8c) to head (f521943).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
ntpd/src/daemon/system.rs	0.00%	24 Missing ⚠️
ntpd/src/daemon/config/ntp_source.rs	71.18%	17 Missing ⚠️
ntpd/src/force_sync/algorithm.rs	0.00%	8 Missing ⚠️
ntpd/src/daemon/config/mod.rs	84.44%	7 Missing ⚠️
ntpd/src/daemon/spawn/nts.rs	0.00%	3 Missing ⚠️
ntpd/src/daemon/spawn/nts_pool.rs	0.00%	3 Missing ⚠️
ntpd/src/force_sync/mod.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1764      +/-   ##
==========================================
- Coverage   81.60%   81.53%   -0.08%     
==========================================
  Files          66       66              
  Lines       20671    20789     +118     
==========================================
+ Hits        16869    16950      +81     
- Misses       3802     3839      +37     

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