[RFC0036] Managing Multiple Github Orgs

[beyhan]

This issue tracks the implementation of RFC-0036: Managing Multiple GitHub Organizations. Please create sub-issues for detailed tracking.

Tasks

• Adapt org management to rfc-0036 #1106
• Support multiple orgs in inactive user deletion #1139
• OrgGenerator support for multiple managed orgs #1170

[rkoster]

@drich10 are we ready to onboard the concourse github org? From the automation side we are ready.