Add backend support for /warn command

drizzle/0027_warnings.sql

@@ -0,0 +1,12 @@
+CREATE TABLE "tg_warnings" (
+	"id" integer PRIMARY KEY GENERATED ALWAYS AS IDENTITY (sequence name "tg_warnings_id_seq" INCREMENT BY 1 MINVALUE 1 MAXVALUE 2147483647 START WITH 1 CACHE 1),
+	"target_id" bigint NOT NULL,
+	"admin_id" bigint NOT NULL,
+	"group_id" bigint NOT NULL,
+	"reason" varchar(256),
+	"is_expired" boolean DEFAULT false NOT NULL,
+	"deleted_at" timestamp (0) with time zone,
+	"created_at" timestamp (0) with time zone DEFAULT now() NOT NULL
+);
+--> statement-breakpoint
+CREATE INDEX "warnings_target_idx" ON "tg_warnings" USING btree ("target_id");