feat: init slack integration

[GangGreenTemperTatum]

full integration with Slack API for sending Slack messages when at least one commit triggered by RedFlag is in_scope, sample images attached to validate testing both in CI mode and in batch mode. i also used some custom emojis here which is easy enough to do in Slack

this page in the wiki will also need updating to include the following in the env section: (i don't have permissions)

        slack_token: ${{ secrets.RF_SLACK_TOKEN }}
        slack_channel: ${{ secrets.RF_SLACK_CHANNEL }}

thanks! 🚀