On-Prem Sentry Integration with On-Prem Azure DevOps Server

## Summary

I was very excited to see that sentry integrates so well with Azure DevOps, but was sad to find, after installing Sentry on-prem, that I cannot integrate with my on-prem Azure DevOps server. Looking at the vsts integration code, it looks like most of the code would be the same for integrating with Azure DevOps server, with only a few changes in the authentication method needed (switching from OAuth to a different method that is supported by Azure DevOps Server, such as personal access tokens or another method from https://docs.microsoft.com/en-us/rest/api/azure/devops/?view=azure-devops-rest-6.1#create-the-request). With that in place, it would follow that the rest of the features carry over using the same API calls to the local Azure DevOps instance.

## Motivation

Our company runs our own data center and keeps all data in-house, which necessitates using both on-prem sentry and on-prem devops. Many of the features of Sentry are connected to release management (such as sourcemap parsing and commit linking), which our team would benefit from having available. In addition, having the issue syncing would allow us to prioritize and track bugs more easily.

Thanks for your awesome product and consideration or this new feature!

┆Issue is synchronized with this [Jira Improvement](https://getsentry.atlassian.net/browse/FEEDBACK-1919) by [Unito](https://www.unito.io)