Add the logic to update the risk scores stored in the DB

[vishesh-baghel]

How do we differentiate between a pull request merged on the default branch and when a pull request is merged on other branches?

• The bot will update the risk scores only when the pull request is merged on the default branch because the default branch is the only source of truth as of now.
• There is a merged flag present in the payload on the pull request closed event, which helps in determining that, but there is no information about where the pull request is getting merged to.
• For now, the bot will only look for the merged flag for determining whether the pull request is being merged on the default branch or not.
  • decided by reading about the pull_request closed event details on: https://docs.github.com/en/webhooks/webhook-events-and-payloads?actionType=closed#pull_request