`swh identify` does not show its output recursively when invoked on non-leaf objects such as directories:
```
$ swh identify --no-filename /srv/src/linux/linux-5.9.1/kernel/
swh:1:dir:5f18abc022c8aa2652008ca75314281d552c8498
```
but to compute that output it of course has processed the entire directory recursively, as that is required by Merkle properties.
We should add a classic `-R/--recursive` flag to `swh identify` that requests to //output// recursively all SWHIDs of recursive objects (at the very least directories, but it would make sense also on snapshots and revisions).