Prevent `pantheon-multidev-*` commands on sites that use CI

[dalin-]

It would be great if these commands detected that CI is likely being used (look for directories like .ci, .circleci, etc.), and then ask: "It looks like this site uses continuous integration. Are you sure that you want to manually create/merge a multidev rather than using CI? (y|N)"

[Yuvania]

I going to assign it to myself, I'll be working on this too