Add bounty program workflows

[cguerreroTT]

Adding the following automations that apply only to issues in the bounty program. These workflows are all defined in the tt-github-actions repo, and will look for the bounty tag on issues.

• bounty-terms.yaml
  • Comments a link to the bounty terms and conditions when someone is assigned to an issue.
• bounty-stale.yaml
  • Uses Stale to comment on issues in the bounty program that have not had any updates in the last two weeks. The bot does not close any issues, nor does it mark any PRs as stale.
• bounty-complete.yaml
  • Comments on the bounty issue after it has been closed, notifying the assignee to send an email to me to start the payment process and complete the bounty feedback survey.