Adding Alkira to list of TC users (#4370)

Author: sankee168

docs/index.md

@@ -174,6 +174,7 @@ A huge thank you to our sponsors:
 * [Jenkins](https://www.jenkins.io/) - Integration testing of multiple plugins and the Trilead SSH2 fork maintained by the Jenkins community
   ([query](https://github.com/search?l=Maven+POM&q=org%3Ajenkinsci+testcontainers&type=Code)).
 * [Elastic](https://www.elastic.co) - Integration testing of the Java APM agent
+* [Alkira](https://www.alkira.com/) - Testing of multiple micro-services using Kafka, PostgreSQL, Apache Zookeeper, Etcd and so on.