Add formatting option for trailing comma

See redhat-developer/yaml-language-server#1063, this PR requires that
PR in order to work.

Fixes #1112

Signed-off-by: David Thompson <davthomp@redhat.com>

Author: datho7561

package.json

@@ -148,6 +148,11 @@
           "default": 80,
           "description": "Specify the line length that the printer will wrap on"
         },
+        "yaml.format.trailingComma": {
+          "type": "boolean",
+          "default": true,
+          "description": "Specify if trailing commas should be used in JSON-like segments of the YAML"
+        },
         "yaml.validate": {
           "type": "boolean",
           "default": true,