feat: Create credentials model and graphQL mutation

packages/backend/src/db/migrations/20211011120732_create_credentials.ts

@@ -0,0 +1,18 @@
+import { Knex } from "knex";
+
+export async function up(knex: Knex): Promise<void> {
+  return knex.schema.createTable('credentials', (table) => {
+    table.increments('id');
+    table.string('key').notNullable();
+    table.string('display_name').notNullable();
+    table.text('data').notNullable();
+    table.integer('user_id').references('id').inTable('users');
+    table.boolean('verified').defaultTo(false);
+
+    table.timestamps(true, true);
+  });
+};
+
+export async function down(knex: Knex): Promise<void> {
+  return knex.schema.dropTable('credentials');
+}