Load roles from path from user context

[marcopiraccini]

This to load roles from structured objects that can be loaded from JWT claims, e.g.:

  "resource_access": {
    "rest-api": {
      "roles": [
        "admin",
        "user"
      ]
    },

To support that, a rolePath can be used, specifying a dot-separated path. In this case we would need:

{ 
   (...)
   rolePath: "resource_access.rest-api.roles"
   (...)
}

[mcollina]

Please add it to https://github.com/platformatic/platformatic/blob/main/docs/reference/db/configuration.md#authorization as well.

[mcollina]

lgtm