Update syno_hdd_db.sh

- Added support for M.2 drives on a PCI card, M2Dxx and E10G18-T1 etc.
- Improved flags/options checking and added usage help.
- Can now download the latest script version for you (if you have user home service enabled in DSM).
- Now adds 'support_m2_pool="yes"' line for models that don't have support_m2_pool in synoinfo.conf to (hopefully) prevent losing your SSH created M2 volume when running this script on models that DSM 7.2 Beta does not list as supported for creating M2 volumes.
- Changed Synology model detection to be more reliable (for models that came in different variations).
- Changed checking drive_db_test_url setting to be more durable.

syno_hdd_db.sh

@@ -40,6 +40,8 @@
 # Can now download the latest script version for you (if you have user home service enabled in DSM).
 #
 # Now adds 'support_m2_pool="yes"' line for models that don't have support_m2_pool in synoinfo.conf
+#   to (hopefully) prevent losing your SSH created M2 volume when running this script on models 
+#   that DSM 7.2 Beta does not list as supported for creating M2 volumes.
 #
 # Changed Synology model detection to be more reliable (for models that came in different variations).
 #