chore: rename props with dot separation

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What's changed and what's your intention?

rename scan.startup.timestamp_millis to scan.startup.timestamp.millis for unifying naming manner

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please rename scan.startup.timestamp_millis to scan.startup.timestamp.millis for kafka, pulsar and nats source

there wont be compatibility issue.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (744df85) 68.30% compared to head (fd19b41) 68.31%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #13656   +/-   ##
=======================================
  Coverage   68.30%   68.31%           
=======================================
  Files        1528     1528           
  Lines      262669   262669           
=======================================
+ Hits       179425   179440   +15     
+ Misses      83244    83229   -15     

Flag	Coverage Δ
rust	68.31% <ø> (+<0.01%)	⬆️

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