[Feature/Extensions] Supporting cluster_permissions nomenclature

[DarshitChanpura]

Current security roles model uses cluster_permissions to evaluate Transport Layer actions. This is because the plugins run in-process with OS cluster.
With Extensions being out-of-process entities, they can request OS cluster only via REST APIs.
And so there is a need to authorize these requests at REST layer.

This issue covers authorizing REST request against the legacy and new cluster_permissions model.

E.g: For hello-world sample extension, the endpoint /hello should succeed when either of the following roles are mapped to a user.

legacy_hw_greet:
  reserved: true
  cluster_permissions:
    - 'cluster:admin/opensearch/hw/greet'


extension_hw_greet:
  reserved: true
  cluster_permissions:
    - 'hw:greet'

This enables minimal effort for admin to enable use of extensions.

• Allow registering legacy transport actionName when registering a NamedRoute

[DarshitChanpura]

Done via #2753