Use OpenSearch 2.0.0-alpha1

[qreshi]

Issue #, if available:

Description of changes:

• Bumps OpenSearch version being used from 2.0.0 to 2.0.0-alpha1
• Removes mapping type usage
• Adds -Dbuild.qualifier=alpha1 to the GitHub Actions to ensure we're using alpha for dependencies as well (i.e. common-utils)

The security workflow is still expected to fail for now since the Docker image with security plugin 2.0 is not available yet.

CheckList:
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[qreshi]

A single test failed in the multi-node test workflow. Looks like it's flaky since the workflow passed on a re-run, will include the command to reproduce for debugging:

./gradlew ':alerting:integTest' --tests "org.opensearch.alerting.MonitorRunnerIT.test create ClusterMetricsInput monitor with alert triggered" -Dtests.seed=E212782E26CD39BD -Dtests.security.manager=false -Dtests.locale=es-AR -Dtests.timezone=Europe/Malta -Druntime.java=11
  2> java.lang.AssertionError: This triggerResult should be triggered: {triggered=false, action_results={}, name=UDMtGnrZFB, error=null}