Automatically display default values of options in the help page (#1032)

Fixes #973

test/Spectre.Console.Cli.Tests/Expectations/Help/Command_Hide_Default.Output.verified.txt

@@ -0,0 +1,17 @@
+DESCRIPTION:
+Contains settings for a cat.
+
+USAGE:
+    myapp cat [LEGS] [OPTIONS] <COMMAND>
+
+ARGUMENTS:
+    [LEGS]    The number of legs
+
+OPTIONS:
+    -h, --help               Prints help information
+    -a, --alive              Indicates whether or not the animal is alive
+    -n, --name <VALUE>
+        --agility <VALUE>    The agility between 0 and 100
+
+COMMANDS:
+    lion <TEETH>    The lion command