Add k6 to adopted tools

radar/tools/k6.md

@@ -0,0 +1,21 @@
+---
+title: "K6"
+ring: adopt
+quadrant: "tools"
+tags: [loadtesting, performance]
+---
+
+[K6](https://k6.io/) is an open-source load testing tool designed for testing the
+performance of APIs, microservices, and websites. It allows developers to create
+and run load tests using JavaScript. K6 is built for modern development workflows and
+integrates well with CI/CD pipelines. It provides a command-line interface (CLI) for running tests
+locally or in the cloud, and it offers a cloud service for distributed load testing.
+
+## Use cases
+
+K6 helps with stressing infrastructure and applications to identify performance bottlenecks,
+ensuring that systems can handle expected traffic loads, and validating the scalability of applications.
+
+## Reference of usage in our organization
+
+- [IO Load Tests](https://github.com/pagopa/io-load-test/blob/9b90df0433d3510ae467c08584aedbe214548208/apps/io-test-e2e/src/utils/config.ts#L45)