[FEATURE] Enable workflow level auth

**Is your feature request related to a problem? Please describe.**
Imagine a workflow that does multiple actions with GitHub. Currently you have to set up the auth on every step that does this. While Pipedream makes this easy by remembering existing connections, there should be a "workflow" level way to provide authentication information.

**Describe the solution you'd like**
Add the ability to auth to a service at the workflow level.

**Do you have a workaround?**
Nope, but you can easily auth per step.

**Comparable features in other tools?**
None