Demonstrate empty pre- and post- checks in Postgres mutations (#707)

Co-authored-by: Sean Park-Ross <[email protected]>

docs/getting-started/build/_databaseDocs/_postgreSQL/_08-mutate-data.mdx

@@ -97,6 +97,35 @@ definition:
                   literal: b1358c05-a457-41e7-b77e-56efce2cdd06
 ```
 
+If we don't wish to provide any checks at this time, we can provide the following:
+
+```hml
+value:
+  booleanExpression:
+    and: []
+```
+
+For example, used here as both `pre-` and `post-` checks on an update mutation:
+
+```hml
+kind: CommandPermissions
+version: v1
+definition:
+  commandName: V2UpdateUsersById
+  permissions:
+    - role: admin
+      allowExecution: true
+      argumentPresets:
+        - argument: preCheck
+          value:
+            booleanExpression:
+              and: []
+        - argument: postCheck
+          value:
+            booleanExpression:
+              and: []
+```
+
 #### Step 4. Build and run
 
 After editing the `.hml` files of your models, create a new build of our supergraph: