[time_table] adding support for URLs / links (#3600)

Using Mustache templating and providing {{ metric }} as well as
{{ ...formData }} as context.

superset/assets/javascripts/explore/stores/visTypes.js

@@ -379,6 +379,7 @@ export const visTypes = {
         controlSetRows: [
           ['groupby', 'metrics'],
           ['column_collection'],
+          ['url'],
         ],
       },
     ],
@@ -386,6 +387,11 @@ export const visTypes = {
       groupby: {
         multiple: false,
       },
+      url: {
+        label: t(
+          "Templated link, it's possible to include {{ metric }} " +
+          'or other values coming from the controls.'),
+      },
     },
   },