Make AccessCredential provider_default and credential types nullable. (#259)

Unless we mark this as nullable, our generated code on the server side
cannot easily discern between a user wanting to set a credential to
not be the default (i.e. `"provider_default": false`) vs. not changing
the default status at all (no `provider_default` field).

We need similar support for our credential types as well.

Author: thetorpedodog

openapi-v2.yaml

@@ -550,7 +550,7 @@ definitions:
       provider_default:
         description: "True if this is the namespace's default credential to be used when connecting to the given cloud provider. There can be at most one default for each unique provider."
         type: boolean
-        x-omitempty: true
+        x-nullable: true
       created_at:
         description: "Time when the credential was created (rfc3339)"
         type: string
@@ -570,7 +570,7 @@ definitions:
             $ref: "#/definitions/AWSCredential"
           azure:
             $ref: "#/definitions/AzureCredential"
-  
+
   AccessCredentialsData:
     description: Object including credentials and pagination metadata
     type: object
@@ -587,6 +587,7 @@ definitions:
   AWSCredential:
     description: "Credential information to access Amazon Web Services"
     type: object
+    x-nullable: true
     x-omitempty: true
     properties:
       access_key_id:
@@ -601,7 +602,8 @@ definitions:
   AzureCredential:
     description: "Credential information to access Microsoft Azure. Each supported property is the snake_case version of its name in an Azure Storage connection string."
     type: object
-    x-omitempty: True
+    x-nullable: true
+    x-omitempty: true
     properties:
       account_name:
         description: "The name of the Azure account to access"