[New] POST /account/settings/managed-enable (#122)

* Added POST /account/settings/managed-enable endpoint

* Update description

Update CLI action and CLI example

Author: hzoppetti

openapi.yaml

@@ -1557,6 +1557,42 @@ paths:
             linode-cli account settings-update \
               --longview_subscription longview-30 \
               --network_helper false
+  /account/settings/managed-enable:
+    x-linode-cli-command: account
+    post:
+      x-linode-grant: read_write
+      tags:
+      - Account
+      summary: Enable Linode Managed
+      description: >
+        Enables Linode Managed for the entire account and sends a welcome email to the account's associated
+        email address. Linode Managed can monitor any service or software stack reachable over TCP or HTTP. See
+        our [Linode Managed guide](https://linode.com/docs/platform/linode-managed/)
+        to learn more.
+      operationId: enableAccountManged
+      x-linode-cli-action: enable-managed
+      security:
+      - personalAccessToken: []
+      - oauth:
+        - account:read_write
+      responses:
+        '200':
+          description: Managed services enabled for account.
+          content:
+            application/json:
+             schema:
+               type: object
+        default:
+          $ref: '#/components/responses/ErrorResponse'
+      x-code-samples:
+        - lang: Shell
+          source: >
+            curl -H "Authorization: Bearer $TOKEN" \
+                -X POST \
+                https://api.linode.com/v4/account/settings/managed-enable
+        - lang: CLI
+          source: >
+            linode-cli account enable-managed
   /account/transfer:
     x-linode-cli-command: account
     get: