Add Admin module and entity

backend/libs/database/admin.entity.ts

@@ -0,0 +1,11 @@
+import { Entity, PrimaryColumn } from 'typeorm';
+
+@Entity()
+export class Admin {
+    constructor(props?: Partial<Admin>) {
+        Object.assign(this, props);
+    }
+
+    @PrimaryColumn()
+    public id!: string;
+}