docs(filemanager): add link to null version id docs

lib/workload/stateless/filemanager/database/migrations/0002_add_s3_object_table.sql

@@ -25,7 +25,7 @@ create table s3_object (
     -- The key of the object.
     key text not null,
     -- The version id of the object. A 'null' string is used to indicate no version id. This matches logic in AWS which
-    -- also returns 'null' strings.
+    -- also returns 'null' strings. See https://docs.aws.amazon.com/AmazonS3/latest/userguide/versioning-workflows.html
     version_id text not null default 'null',
     -- When this object was created. A null value here means that a deleted event has occurred before a created event.
     created_date timestamptz default null,