DM-45133: Set xtype on timestamp columns

[JeremyMcCormick]

• Add a validator to automatically set the votable_xtype to "timestamp" on Felis timestamp columns.

Checklist

• Ran Jenkins
• Added a release note for user-visible changes to docs/changes

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.37%. Comparing base (c5a10cf) to head (b7a3565).

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #117      +/-   ##
==========================================
+ Coverage   92.35%   92.37%   +0.02%     
==========================================
  Files          21       21              
  Lines        2615     2623       +8     
  Branches      257      258       +1     
==========================================
+ Hits         2415     2423       +8     
  Misses        127      127              
  Partials       73       73              

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[gpdf]

@JeremyMcCormick Is this reviewable at this time?