[Onboarding] - Slack integration for team join request as team lead

[getheobald]

Description

As a team lead, I want a slack notification when new members request to join my team that I can automatically approve or deny via emoji reaction within slack

Acceptance Criteria

• When a new member submits a team join request, the team lead receives a slack notification
• Notification includes member’s name and the team they’re requesting to join
• Team lead can react with an emoji to approve or deny the request from slack
• Approval/denial in Slack updates the member’s dashboard the same as approval/denial in Finishline
• If Slack notification fails, request still appears in Finishline for manual approval

Proposed Solution

Slack thread brought up ephemeral messages but I'm not sure if that's right... but it should be similar to Slack attendance functionality

Mocks

No response