bug: Fixed linode-cli databases types output

Requires linode/linode-cli#298
Closes linode/linode-cli#297

The `x-linode-cli-nested-list` spec extension must reference a property
of the returned schema, which it currently does not.  Additionally, this
particular schema includes three related nested lists; I've added
support for all of them in the linked CLI change, and the new structure
here supports that.

Author: Dorthu

openapi.yaml

@@ -5548,20 +5548,26 @@ paths:
           description: Returns a paginated list of all Managed Database types.
           content:
             application/json:
-              x-linode-cli-nested-list: cluster_size
+              x-linode-cli-nested-list: engines.mysql, engines.postgresql, engines.mongodb
               x-linode-cli-use-schema:
                 type: object
                 properties:
                   id:
                     x-linode-cli-display: 1
                   label:
                     x-linode-cli-display: 2
-                  cluster_size.quantity:
-                    x-linode-cli-display: 3
-                  cluster_size.price.hourly:
-                    x-linode-cli-display: 4
-                  cluster_size.price.monthly:
-                    x-linode-cli-display: 5
+                  _split:
+                    x-linode-cli-display: 2.5
+                  engines:
+                    properties:
+                       quantity:
+                        x-linode-cli-display: 3
+                       price:
+                         properties:
+                           hourly:
+                             x-linode-cli-display: 4
+                           monthly:
+                             x-linode-cli-display: 5
               schema:
                 allOf:
                 - $ref: '#/components/schemas/PaginationEnvelope'
@@ -5608,20 +5614,26 @@ paths:
           description: Returns a single Managed Database type.
           content:
             application/json:
-              x-linode-cli-nested-list: cluster_size
+              x-linode-cli-nested-list: engines.mysql, engines.postgresql, engines.mongodb
               x-linode-cli-use-schema:
                 type: object
                 properties:
                   id:
                     x-linode-cli-display: 1
                   label:
                     x-linode-cli-display: 2
-                  cluster_size.quantity:
-                    x-linode-cli-display: 3
-                  cluster_size.price.hourly:
-                    x-linode-cli-display: 4
-                  cluster_size.price.monthly:
-                    x-linode-cli-display: 5
+                  _split:
+                    x-linode-cli-display: 2.5
+                  engines:
+                    properties:
+                       quantity:
+                        x-linode-cli-display: 3
+                       price:
+                         properties:
+                           hourly:
+                             x-linode-cli-display: 4
+                           monthly:
+                             x-linode-cli-display: 5
               schema:
                 $ref: '#/components/schemas/DatabaseType'
         default: