`src validate install` requires GH token no matter what

Created by: scjohns

Overview

In the src validate install command, you are able to define a custom spec to run for your validations. This spec can do a number of different things, including search across repos that already exist, create an insight, or add an external service. In this process, we validate that the user has the variable SRC_GITHUB_TOKEN set in their shell, but that token not be required depending on the spec.

Proposed Behavior

• Fail gracefully if an action requiring a GH token (Ex: adding an external service) is needed and no token is set.
• Allow for searching across repos that already exist on the instance
• Do not attempt to clone or validate anything related to external services if there's no spec to create one.