I'm not sure what you want to accomplish by saying "Enable Gitflow". As per my understanding, Gitflow is a workflow that your team can follow as your SCM guideline. It's not something configurable, it's something you and your developers do through out your development. Atlassian have created a very good documentation about this on the link below.
Some part of this may need some add-ons or tweaking branch permissions and that's it. I think that's the "Enable" part you are talking about here.
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