Add configuration flag to disable system index permissions

[peternied]

Problem:

System index permissions allow access to data on clusters that was previously not accessible. For services that operate managed OpenSearch clusters they could want to restriction based on custom index / plugins configuration.

Proposed solution:

Check for a value in the security config something like "system index permissions disabled".

• For existing clusters that migrate to the latest version, the features should be disabled by default.
• For new clusters, the feature should be enabled by default.

[stephen-crawford]

[Triage] Hi @peternied, this sounds like a good request considering the discussions around system indices. I think that @cwperks will have some suggestions on what may fall under this as well and may want to follow up here.