feat: Add push/email notification support for SLA (#9140)

* feat: update SLA evaluation logic

* Update enterprise/app/services/sla/evaluate_applied_sla_service.rb

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

* chore: refactor spec to bring down expecations in a single block

* chore: fix process_account_applied_sla spec

* chore: add spec to test multiple nrt misses

* feat: persist sla notifications

* feat: revert persist sla notifications

* feat: add SLA push/email notification support

* chore: refactor sla_status to include active_with_misses

* chore: add support for sla push/email notifications

* chore: refactor

* chore: add liquid templates

* chore: add spec for liquid templates

* chore: add spec for sla email notifications

* chore: add spec for SlaPolicyDrop

* chore: refactor to ee namespace

* chore: set enterprise test type to mailer

* feat: enable sla notification settings only if SLA enabled

* chore: refactor

* chore: fix spec

---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

enterprise/app/models/enterprise/application_record.rb

@@ -0,0 +1,5 @@
+module Enterprise::ApplicationRecord
+  def droppables
+    super + %w[SlaPolicy]
+  end
+end