[Backport 2.x] DocLevel Monitor - generate findings when 0 triggers

[opensearch-trigger-bot]

Backport 4ba7d42 from #856

[codecov-commenter]

Codecov Report

Merging #895 (9175634) into 2.x (493139e) will increase coverage by 0.04%.
Report is 31 commits behind head on 2.x.
The diff coverage is 85.18%.

❗ Current head 9175634 differs from pull request most recent head f19be3b. Consider uploading reports for the commit f19be3b to get more accurate results

@@             Coverage Diff              @@
##                2.x     #895      +/-   ##
============================================
+ Coverage     76.64%   76.68%   +0.04%     
  Complexity      116      116              
============================================
  Files           125      125              
  Lines          7061     7078      +17     
  Branches       1034     1036       +2     
============================================
+ Hits           5412     5428      +16     
- Misses         1123     1125       +2     
+ Partials        526      525       -1     

Files Changed	Coverage Δ
.../opensearch/alerting/DocumentLevelMonitorRunner.kt	83.01% <85.18%> (-0.38%)	⬇️

... and 3 files with indirect coverage changes

[lezzago]

This was merged as part of #907