schema: add "pending" field to GitHub code host connection

Created by: unknwon

We need a pending state for connecting code hosts through GitHub App if GitHub org admin approval is required. As this is very specific to the GitHub App flow, adding an extra field to the GitHub code host connection schema takes the minimal effort.

Due to the fact that the "repos": [] field is empty, our repo syncing would effectively do nothing despite at this point, the "token" value is invalid.

Test plan

JSON schema validation.

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Jira: CLOUD-310