Drone

[scm] support disabling verification on scm triggers

Currently when creating the hooks on the scm, Drone doesn’t allow for ssl verification to be disabled despite most of the functionality having already been added.

I’d like to propose adding a new config option (DRONE_SCM_HOOK_SKIP_VERIFY as an example), that will set it. The changes should be minimal (mostly in the HookService and propagating the config through)