fix(dav): only list top-level groupfolders

[skjnldsv]

You can have multiple folders with the same name
You can also have many of those same names nested into other sub-groupfolders.
Example:

├── TeamFolder1
│   ├── TeamFolder1
│   ├── TeamFolder2
│   ├── TeamFolder3
│   ├── TeamFolder4
│   └── TeamFolder5
└── TeamFolder2
    ├── TeamFolder1
    ├── TeamFolder2
    ├── TeamFolder3
    ├── TeamFolder4
    └── TeamFolder5

Resolution:

1. We now only show top-level groupfolders, as clicking one will show the children anyway
2. We now group them by source name, and use the groupfolder ID instead of the mountpoint to generate their source. Making them truly unique

[provokateurin]

I get the idea, but a frontend only fix is probably not enough. We also need to fix it in some way for the clients and they should all have the same experience, so a backend fix seems like a much better solution.

[skjnldsv]

@provokateurin yes and no, there are multiple endpoints used here.
This one is the dedicated groupfolder listing endpoint, so a fix on the front is actually needed anyway.

Also, while I agree we need a backend fix, I cannot wait for a deeper refactor of our code.
Mitigating the issue is the priority