Detail path definition conflicts

[davidbrochart]

Problem

Currently, when two or more plugins define an endpoint with the same path, we get an error message like:

[E 2021-10-06 15:41:06 fps] Redefinition of path(s) ['/lab/api/themes', '/'] is not allowed.

We don't know which plugins define the same endpoint.

Proposed Solution

It would be nice to have a more detailed error message, like:

[E 2021-10-06 15:41:06 fps] Redefinition of path(s) is not allowed:
[E 2021-10-06 15:41:06 fps] Path '/lab/api/themes' is defined by: JupyterLab, RetroLab.
[E 2021-10-06 15:41:06 fps] Path '/' is defined by: JupyterLab, RetroLab.

[adriendelsalle]

👍