Recently had a need for something like this and Gitlab ended up losing to BitBucket Server which we bought along with JIRA and Confluence. Gitlab seems like a nice, light solution, but their issue tracker ain't JIRA.
My company is using atlassian products heavily and I was surprised to find very good support for GitLab. I run it locally and love it and I'm pushing to use it at work.
Our aim was to provide an at the glance view of the development status (# of commits, branches, pull requests and their status, builds and deployments) with the option to see more detailed information right within JIRA. And of course you can create a new branch right from your JIRA issue.
Lastly, ensuring that the data is 100% reliable and up to date was an important consideration which most of the basic webhook integrations simply ignore.
Take a look at the documentation, which provides a great overview of the integration: https://confluence.atlassian.com/jira/viewing-the-code-devel...