github app: auto-create labels upon installation

[jamesdlevine]

Ideally the user should not have to create the labels themselves when they install the application.

• pdd, architecture, bug, fix, change, generate, connect
• consider removing the requirement to use the pdd label (it's inconvenient) and instead auto create unique labels:
  • example: pdd-architecture, pdd-bug, pdd-fix, pdd-change, pdd-generate, pdd-connect