app: fix custom session routes with path prefix

[jamaljsr]

Summary

When running litd using a path-prefix (ex: PUBLIC_URL=/lit), the route navigation is not working properly. It navigates to /connect instead of /lit/connect. The fix was simply to ensure the new route is always prefixed with the PUBLIC_URL env var.

Screenshots

This is what currently happens when using a path prefix on master

litd-path-prefix-custom-session-broken.mp4

This shows the functioning flow when using this PR

litd-path-prefix-custom-session.mp4

Steps to Test

1. Start the app with a path prefix

   cd app/
   PUBLIC_URL=/lit yarn start
   

2. Navigate to http://localhost:3000/lit/connect
3. Enter a name and choose "Custom" for the Permissions and click Next
4. Modify the permissions however you like and click Submit
5. Confirm you are redirected back to the LNC page without hitting any invalid url paths
6. Restart the app without the path prefix

   yarn start
   

7. Navigate to http://localhost:3000/connect (removed /lit prefix)
8. Repeat steps 3-5 to confirm the flow works fine without a path prefix specified

Related Issues & Pull Requests

Closes #1058

[itsrachelfish]

tACK, confirmed I was able to navigate to the LNC custom settings page using a PUBLIC_URL prefix

[ViktorT-11]

Nice, thanks for the fix 🙏. LGTM!