Make dashboard app port configurable

[jsbrain]

https://github.com/cube-js/cube.js/blob/7d2cf5469ea62fe20f18fc60044e0fd88d233ecd/packages/cubejs-server-core/src/core/server.ts#L414

Apparently, the dashboard app port is hardcoded which is a bummer if one already has an app running on port 3000.

Manually "hacking" the port in the package.json to "react scripts start --port 3111" does start the dashboard on the other port but the start command will be messy as my logs show:

cube_1   | 
cube_1   | > dashboard-app@0.1.0 start /cube/conf/dashboard-app
cube_1   | > react-scripts start --port 3111 "--port" "3000" "--host" "0.0.0.0"
cube_1   | 

Also it doesn't help much as the dashboard while starting on port 3111 won't be connected to the playground.

This means one always has to reconfigure a potentially already configured application to get the dashboard app up and running and working with the playground.

Is there any specific reason why it's implemented like that or am I missing something here?

[jsbrain]

Having CUBEJS_DASHBOARD_APP_PORT would be amazing and easy to implement (I think)?

[github-actions]

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[igorlukanin]

Dashboard app generation was removed from Cube Core long time ago.