System indices should be able to bypass restricted index auto creation

[jaymode]

System indices are needed by Elasticsearch and the stack so we should always be able to create them. Currently the action.auto_create_index setting governs whether any index can be auto created and could prevent system indices from being created. This behavior allows a user to unknowingly set a value for this setting that prevents the operation of certain features that are built-in to the product and adds to the steps needed to set up features and leads to frustration.

As part of the system indices effort we need to ensure that system indices can be automatically created from an index request.

[elasticmachine]

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