Is your feature request related to a problem? Please describe.
Remove .opendistro-alerting-alert* indices from system-indices configuration by default.

Describe the solution you'd like
.opendistro-alerting-alert* indices contains current and historical alerts. Currently, .opendistro-alerting-alert* indices are configured as system-index by default. To access these indices, you must authenticate with an admin certificate. Though system-indices provide greater privileges requirements to directly access these indices, but at the same time users can't build visualizations and dashboards on top of these indices.

Proposal:

Remove .opendistro-alerting-alert* indices from system-indices configuration by default. Still the access to these indices are controlled by roles. This would enable building visualizations and dashboards on top of these indices.
And at the same time, secure access is controlled by security roles rather than system-indices.

Describe alternatives you've considered
Edit OpenSearch.yml file and remove .opendistro-alerting-alert* from opendistro_security.system_indices.indices.

Additional context
Similar proposal for .opendistro-anomaly-results* indices which store results of the Anomaly Detection plugin generated results.