add docs for ceph_status

docs/20_Checks/check_ceph_status.md

+# Check Ceph Status
+
+## Introduction
+
+**check_ceph_sttaus** is a plugin to show ceph status.
+It switches the state in dependency of the HEALTH_* value.
+
+## Requirements
+
+* `ceph` binary and sudo permission on it to get the information
+
+## Syntax
+
+```txt
+______________________________________________________________________
+
+DEV_CHECK_CEPH_STATUS 
+v1.5
+
+(c) Institute for Medical Education - University of Bern
+Licence: GNU GPL 3
+______________________________________________________________________
+
+Show ceph health status.
+The state of the check switches to warning if HEALTH_WARN was detected
+and is error of other HEALTH values than HEALTH_WARN or HEALTH_OK.
+
+In the output is the complete output of the command "ceph status".
+
+SYNTAX:
+check_ceph_status
+
+OPTIONS:
+    -h or --help   show this help.
+
+```
+
+### Parameters
+
+(none)
+
+## Examples
+
+`$ check_ceph_status` returns
+
+```txt
+OK: Ceph status is HEALTH_OK
+
+  cluster:
+    id:     12345678-68e3-4c21-bf95-4b5f802f81a4
+    health: HEALTH_OK
+ 
+  services:
+    mon: 3 daemons, quorum cephmon1,cephmon2,cephmon3 (age 2w)
+    mgr: cephmon3(active, since 2w), standbys: cephmon2, cephmon1
+    osd: 30 osds: 30 up (since 2w), 30 in (since 5w)
+ 
+  data:
+    pools:   3 pools, 161 pgs
+    objects: 608.44k objects, 2.3 TiB
+    usage:   6.9 TiB used, 47 TiB / 54 TiB avail
+    pgs:     161 active+clean
+ 
+  io:
+    client:   896 KiB/s rd, 12 MiB/s wr, 372 op/s rd, 401 op/s wr
+
+```
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