Decide on deployment: atlantis user, atlantis comment, github app

[lkysow]

Installation Options

• install webhook on individual repositories
• install webhook on organization
• install as oauth app
• install as Github App

Can also choose between listening for comments mentioning an @atlantis user or just the string "atlantis"

Webhooks require a two step installation: create a user and then add the webhook to the repo
OAuth could be a one-step solution but we'd need to support oauth flow
I don't think Github Apps will work for Github Enterprise. CircleCI's instructions ask people to add it as an OAuth App. I haven't done a ton of research into this. Apps are nice because they automatically get a bot user associated with them, but I think it's probably over complicated for what we need.

So I think we should recommend adding as a git hook on the organization and also setting up an Atlantis user.

We could use the mentions API but I think we should still use webhooks so we can do things like auto-planning in the future (before atlantis is mentioned). We can also support both @atlantis and atlantis.