Change github deployment role to pre/post deployment step

[thatbudakguy]

see for example https://github.com/pulibrary/princeton_ansible/blob/540e2136fdec4becd1336dd1c68ffbf41296de95/playbooks/approvals_production.yml#L12-L21

unfortunately it looks like there's no modules published on ansible galaxy to handle this (we might consider publishing one, actually, if we get it working well). they do have ones for creating/updating github releases, but not deployments.

some digging reveals that pre_tasks and post_tasks are not special at all - they just run arbitrary tasks at the specified time, and will not be run if the playbooks fail. i think the way to approach this is to:

• consolidate our create/complete/fail deployment tasks into a single github role (along with cloning)
• use include to pull the tasks from this role into each playbook as pre_tasks and post_tasks
• make sure the tasks include the special always tag so they run regardless of playbook failure
• also add a new tag github_deploy (or similar) to the tasks so that we can easily turn off github deploys when running the playbook with --skip-tag=github_deploy or similar. see this article for more info on this approach.