volume: add support for non-volatile upperdir,workdir for overlay volumes

Often users want their overlayed volumes to be `non-volatile` in nature
that means that same `upper` dir can be re-used by one or more
containers but overall of nature of volumes still have to be `overlay`
so work done is still on a overlay not on the actual volume.

Following PR adds support for more advanced options i.e custom `workdir`
and `upperdir` for overlayed volumes. So that users can re-use `workdir`
and `upperdir` across new containers as well.

Usage
```console

$ podman run -it -v myvol:/data:O,upperdir=/path/persistant/upper,workdir=/path/persistant/work alpine sh

```

Signed-off-by: Aditya R <arajan@redhat.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/docs/source/markdown/podman-run.1.md b/docs/source/markdown/podman-run.1.md
index 241cb6d95..59f36f67d 100644
--- a/docs/source/markdown/podman-run.1.md
+++ b/docs/source/markdown/podman-run.1.md
@@ -1394,6 +1394,10 @@ directory will be the lower, and the container storage directory will be the
 upper. Modifications to the mount point are destroyed when the container
 finishes executing, similar to a tmpfs mount point being unmounted.
 
+  For advanced users overlay option also supports custom non-volatile `upperdir` and `workdir`
+for the overlay mount. Custom `upperdir` and `workdir` can be fully managed by the users themselves
+and `podman` will not remove it on lifecycle completion. Example `:O,upperdir=/some/upper,workdir=/some/work`
+
   Subsequent executions of the container will see the original source directory
 content, any changes from previous container executions no longer exist.