Rename table from 't0' to 't1' and modify 'username'

Changed table name from 't0' to 't1' and removed NOT NULL constraint on 'username'.

Author: adela-bytebase

migrations-semver/1.0.2_create_t1.sql

@@ -0,0 +1,4 @@
+CREATE TABLE "public"."t1" (
+    "id" serial PRIMARY KEY,
+    "username" text
+);