[payment-endpoint] Revise handling of GitHub plans

[geropl]

payment-endpoint currently logs excessive warnings/errors during regular syncing. We should have a closer look and check if the logic is still correct, or we can remove/simplify, or simply disable logging.

Reference: https://console.cloud.google.com/errors?service=payment-endpoint&time=P30D&order=COUNT_DESC&resolution=OPEN&resolution=ACKNOWLEDGED&project=gitpod-191109&folder&organizationId&supportedpurview=project

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.