docs: add default environment variables available in hosted enviroment (supabase#38666)

Author: laktek

apps/docs/content/guides/functions/secrets.mdx

@@ -14,6 +14,12 @@ Edge Functions have access to these secrets by default:
 - `SUPABASE_SERVICE_ROLE_KEY`: The `service_role` key for your Supabase API. This is safe to use in Edge Functions, but it should NEVER be used in a browser. This key will bypass Row Level Security
 - `SUPABASE_DB_URL`: The URL for your Postgres database. You can use this to connect directly to your database
 
+In a hosted environment, functions have access to the following environment variables:
+
+- `SB_REGION`: The region function was invoked
+- `SB_EXECUTION_ID`: A UUID of function instance ([isolate](/docs/guides/functions/architecture#4-execution-mechanics-fast-and-isolated))
+- `DENO_DEPLOYMENT_ID`: Version of the function code (`{project_ref}_{function_id}_{version}`)
+
 ---
 
 ## Accessing environment variables