restart Field Report numbering at 1 each event

[srabraham]

this makes FRs consistent with Incidents

FYI @wsanchez @virtual256 @kimballa

it'd be better still if we let the DB assign IDs directly using autoincrement, but that's a problem for another day. This just makes the incident and FR approaches the same

#1505

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.72%. Comparing base (9f68e44) to head (169fbe0).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1506      +/-   ##
==========================================
- Coverage   69.74%   69.72%   -0.03%     
==========================================
  Files         181      181              
  Lines        8985     8985              
  Branches     1489     1489              
==========================================
- Hits         6267     6265       -2     
- Misses       2613     2614       +1     
- Partials      105      106       +1     

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