Refactor JiraConnect dev info

What does this MR do and why?

This MR doesn't change the logic of how we construct the Jira dev info API call. It is only a refactoring to make it better testable.

Why is this needed?

I would like to reduce Gitaly N+1 requests by providing an option to exclude files from the commit entity. However, it is difficult to test the behavior of the dev info request.

MR acceptance checklist

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