Setting up GitLab Runner For Continuous Integration

What this post added

This post details the setup and configuration of GitLab Runner with its Docker executor for continuous integration. It covers creating a `.gitlab-ci.yml` file to define build environments and scripts, including the use of Docker images and services for dependencies like PostgreSQL. It also explains how to use shared runners and how to install and register a specific runner on a private server. Furthermore, it introduces caching for `node_modules` to speed up builds and demonstrates how to add concurrency by splitting tests into multiple jobs and increasing the runner's concurrent setting.