prevent username changing

packages/builder/src/components/backend/DataTable/RowFieldControl.svelte

@@ -1,5 +1,7 @@
 <script>
   import { Input, Select, Label, DatePicker, Toggle } from "@budibase/bbui"
+  import { backendUiStore } from "builderStore"
+  import { TableNames } from "constants"
   import Dropzone from "components/common/Dropzone.svelte"
   import { capitalise } from "../../../helpers"
   import LinkedRowSelector from "components/common/LinkedRowSelector.svelte"
@@ -9,6 +11,7 @@
 
   $: type = meta.type
   $: label = capitalise(meta.name)
+  $: userTableSelected = $backendUiStore.selectedTable?._id === TableNames.USERS
 </script>
 
 {#if type === 'options'}
@@ -30,5 +33,11 @@
 {:else if type === 'link'}
   <LinkedRowSelector bind:linkedRows={value} schema={meta} />
 {:else}
-  <Input thin {label} data-cy="{meta.name}-input" {type} bind:value />
+  <Input
+    thin
+    {label}
+    data-cy="{meta.name}-input"
+    {type}
+    bind:value
+    disabled={userTableSelected} />
 {/if}