This would allow writing configurations like:
```
storage:
- filter
- buffer
- cls: remote
args:
url: http://swh-storage:5002/
```
instead of:
```
storage:
cls: filter
args:
storage:
cls: buffer
args:
storage:
cls: remote
args:
url: http://swh-storage:5002/
```
(example from D2275)
I think I gives more readable configs, but on the other hand it adds
more code to maintain. So I'm not sure if this is a good idea.
Comments welcome.