Redirect logged in users who click "Sign in" to sourcegraph.com/cody/manage

[chenkc805]

Current behavior:

• Go to sourcegraph.com as a logged in user
• Click "Get Cody for free" and see modal (see screenshot)
• Click "Sign in" at the very bottom where it says "Already have an account?"
• 🐛 See that you get redirected to /search.
  • Desired behavior: Redirect the logged in user to sourcegraph.com/cody/manage instead

[gitstart-app[bot]]

Here is the GitStart Ticket for this issue: https://clients.gitstart.com/sourcegraph/3436/tickets/SGM-6843