Use notification snapshot for integ test

[lezzago]

Issue #, if available:
N/A
Description of changes:

• Use notification snapshot for integ test
• This improves stability for the tests when ci builds are not done.
  CheckList:
  [X] Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov-commenter]

Codecov Report

Merging #822 (b7ad445) into 2.x (ba54edd) will increase coverage by 0.11%.
The diff coverage is 66.66%.

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@@             Coverage Diff              @@
##                2.x     #822      +/-   ##
============================================
+ Coverage     75.49%   75.61%   +0.11%     
  Complexity      116      116              
============================================
  Files           125      125              
  Lines          6851     6868      +17     
  Branches       1028     1031       +3     
============================================
+ Hits           5172     5193      +21     
+ Misses         1156     1151       -5     
- Partials        523      524       +1     

Impacted Files	Coverage Δ
...lin/org/opensearch/alerting/alerts/AlertIndices.kt	73.25% <0.00%> (-0.61%)	⬇️
.../alerting/transport/TransportIndexMonitorAction.kt	54.27% <0.00%> (ø)
...opensearch/alerting/util/DocLevelMonitorQueries.kt	72.24% <50.00%> (+0.55%)	⬆️
.../opensearch/alerting/DocumentLevelMonitorRunner.kt	80.27% <66.66%> (+0.54%)	⬆️
...n/kotlin/org/opensearch/alerting/AlertingPlugin.kt	93.75% <100.00%> (+0.03%)	⬆️
...ensearch/alerting/MonitorRunnerExecutionContext.kt	100.00% <100.00%> (ø)
...in/org/opensearch/alerting/MonitorRunnerService.kt	80.00% <100.00%> (+0.40%)	⬆️
.../kotlin/org/opensearch/alerting/util/IndexUtils.kt	76.27% <100.00%> (+5.43%)	⬆️
...ain/kotlin/org/opensearch/alerting/AlertService.kt	80.00% <0.00%> (+0.46%)	⬆️
... and 2 more

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