Support per organization webhook

[oded-dd]

Change Request

Tell us about your environment

• Concourse version:
  v5.0.0
• github-webhook-resource version:
  v1.5.0

Describe your change request

The problem you want to solve:
Be able to configure webhook per organization in addition to webhook per repository

Your take on the correct solution to problem:

Do you plan to submit a pull request to implement this change?