extract interaction alert check to it's own class

fixes CNVS-12405

test plan:
regression test alerts sent out based on Submission Comments and
Conversation Messages

Change-Id: Ibd145fe07b7c23180bf855afa96c1d4e47459409
Reviewed-on: https://gerrit.instructure.com/33300
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Jeremy Putnam <jeremyp@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>