Discover AEN with sysobjectid instead of sysdescr (#15482)

* Discover AEN with sysobjectid instead of sysdescr

According to: 
- https://docs.vmware.com/en/VMware-Smart-Assurance/10.1.11/ncm-dsr-support-matrix-33HF1/GUID-C98227E4-830C-4044-894C-157D3CE71058.html
- https://oid-rep.orange-labs.fr/get/1.3.6.1.4.1.22420.1.1
- the fact that the AEN yaml file use ACD-DESC-MIB which is under this same OID (https://www.circitor.fr/Mibs/Html/A/ACD-DESC-MIB.php)

I'm changing the discovery mode, so it won't prevent devices with AEN in their sysname to be properly discovered.
Solve https://github.com/librenms/librenms/issues/15476

* Change to sysdescr_regex

* Add regex delimiters

includes/definitions/aen.yaml

@@ -9,7 +9,8 @@ over:
 mib_dir: accedian
 discovery:
     -
-        sysDescr:
-            - AMN-
-            - AEN-
-            - AMO-
+        sysDescr_regex:
+            - '/^AMN-/'
+            - '/^AEN-/'
+            - '/^AMO-/'
+