GUACAMOLE-610: Add SSH/telnet parameter definitions for maximum scrollback size.

guacamole-ext/src/main/resources/org/apache/guacamole/protocols/ssh.json

@@ -59,6 +59,10 @@
                     "type"  : "ENUM",
                     "options" : [ "", "8", "9", "10", "11", "12", "14", "18", "24", "30", "36", "48", "60", "72", "96" ]
                 },
+                {
+                    "name"  : "scrollback",
+                    "type"  : "NUMERIC"
+                },
                 {
                     "name"    : "read-only",
                     "type"    : "BOOLEAN",

guacamole-ext/src/main/resources/org/apache/guacamole/protocols/telnet.json

@@ -63,6 +63,10 @@
                     "type"  : "ENUM",
                     "options" : [ "", "8", "9", "10", "11", "12", "14", "18", "24", "30", "36", "48", "60", "72", "96" ]
                 },
+                {
+                    "name"  : "scrollback",
+                    "type"  : "NUMERIC"
+                },
                 {
                     "name"    : "read-only",
                     "type"    : "BOOLEAN",