(core) Limiting doc remove permission to owners.

Summary:
Guest editors added to a document were able to remove it. This limits this permission
by allowing only owners of a doc to delete it.

Test Plan: Updated

Reviewers: paulfitz

Reviewed By: paulfitz

Subscribers: dsagal, anaisconce

Differential Revision: https://phab.getgrist.com/D3708

test/gen-server/testUtils.ts

@@ -26,6 +26,19 @@ export function configForUser(username: string): AxiosRequestConfig {
   return config;
 }
 
+/**
+ * Appends a permit key to the given config. Creates a new config object.
+ */
+export function configWithPermit(config: AxiosRequestConfig, permitKey: string): AxiosRequestConfig {
+  return {
+    ...config,
+    headers: {
+      ...config.headers,
+      Permit: permitKey
+    }
+  };
+}
+
 /**
  * Create a new user and return their personal org.
  */