Block direct system index access

[jaymode]

This issue covers the work needed to fully enable blocking direct internal system index access via the REST API. This work depends on at least the following:

• System index deletion API Add an API to remove System Indices #62778
• Tests stop directly accessing system indices Stop accessing System Indices directly in REST tests #62501
• External system indices External system indices #67383
• Enable Enrich to work with System Indices Allow population of Enrich indices to work with System Index protections #62505

[elasticmachine]

Pinging @elastic/es-core-infra (Team:Core/Infra)

[EricDavisX]

Would we also update any API Docs that relate to indices or perhaps a generic note in the docs for apis that hit indices? I ran into internal team docs that noted to a /flush (with no index specified) and when it didn't work i checked the formal docs and didn't see anything calling out that it shouldn't work. might be nice to help call it out as a task in the check-list to update docs.

this is the issue I logged thinking it was Kibana side: elastic/kibana#101294