Declare the endpoint

[maximlt]

The endpoint is obtained from the config filename.

https://github.com/holoviz/lumen/blob/da632cfeee8346991fef772faf54319312cc3642/lumen/dashboard.py#L332

It would be nice to be able to declare the endpoint in the config itself, if set this would take precedence over using the filename.

My use case was trying to deploy the examples which all share the same dashboard.yaml filename, this was causing issues with the app selector (the menu button in the header) which was always navigating to the same page.