api ceph osd: add OSD index, metadata and lv-info

api ceph osd: add OSD index, metadata and lv-info

To get more details for a single OSD, we add two new endpoints:
* nodes/{node}/ceph/osd/{osdid}/metadata
* nodes/{node}/ceph/osd/{osdid}/lv-info

The {osdid} endpoint itself gets a new GET handler to return the index.

The metadata one provides various metadata regarding the OSD.

Such as
* process id
* memory usage
* info about devices used (bdev/block, db, wal)
    * size
    * disks used (sdX)
    ...
* network addresses and ports used
...

Memory usage and PID are retrieved from systemd while the rest can be
retrieved from the metadata provided by Ceph.

The second one (lv-info) returns the following infos for a logical
volume:
* creation time
* lv name
* lv path
* lv size
* lv uuid
* vg name

Possible volumes are:
* block (default value if not provided)
* db
* wal

'ceph-volume' is used to gather the infos, except for the creation time
of the LV which is retrieved via 'lvs'.

Signed-off-by: Aaron Lauterer <a.lauterer@proxmox.com>
Reviewed-by: Dominik Csapak <d.csapak@proxmox.com>
Tested-by:  Dominik Csapak <d.csapak@proxmox.com>