Reapply "CLDC-4497: Allow users with no role to download data (#3360)"

This reverts commit 862f641807.

db/migrate/20260713105230_allow_null_role_in_download_records.rb

@@ -0,0 +1,5 @@
+class AllowNullRoleInDownloadRecords < ActiveRecord::Migration[7.2]
+  def change
+    change_column_null :download_records, :user_role, true
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.2].define(version: 2026_06_18_101455) do
+ActiveRecord::Schema[7.2].define(version: 2026_07_13_105230) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
 
@@ -111,7 +111,7 @@ ActiveRecord::Schema[7.2].define(version: 2026_06_18_101455) do
     t.string "download_filters", null: false
     t.bigint "user_id", null: false
     t.bigint "user_organisation_id", null: false
-    t.integer "user_role", null: false
+    t.integer "user_role"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.index ["user_id"], name: "index_download_records_on_user_id"