Add a matrix_synapse_url_preview_ip_range_blacklist variable

roles/custom/matrix-synapse/templates/synapse/homeserver.yaml.j2

@@ -1131,26 +1131,7 @@ url_preview_enabled: {{ matrix_synapse_url_preview_enabled|to_json }}
 #
 # Note: The value is ignored when an HTTP proxy is in use
 #
-url_preview_ip_range_blacklist:
-  - '127.0.0.0/8'
-  - '10.0.0.0/8'
-  - '172.16.0.0/12'
-  - '192.168.0.0/16'
-  - '100.64.0.0/10'
-  - '192.0.0.0/24'
-  - '169.254.0.0/16'
-  - '192.88.99.0/24'
-  - '198.18.0.0/15'
-  - '192.0.2.0/24'
-  - '198.51.100.0/24'
-  - '203.0.113.0/24'
-  - '224.0.0.0/4'
-  - '::1/128'
-  - 'fe80::/10'
-  - 'fc00::/7'
-  - '2001:db8::/32'
-  - 'ff00::/8'
-  - 'fec0::/10'
+url_preview_ip_range_blacklist: {{ matrix_synapse_url_preview_ip_range_blacklist | to_json }}
 
 # List of IP address CIDR ranges that the URL preview spider is allowed
 # to access even if they are specified in url_preview_ip_range_blacklist.