FEATURE: allow better fidelity for auto linkify, disable most tlds based linkify

New site settings:

enable_markdown_linkify: which is default on, auto links https:// and http:// and mail://

markdown_linkify_tlds: which allows control of what tlds get autolinked for cases such as www.site.com, default is com|net|gov

app/assets/javascripts/pretty-text/engines/discourse-markdown-it.js.es6

@@ -215,10 +215,12 @@ export function setup(opts, siteSettings, state) {
     html: true,
     breaks: opts.discourse.features.newline,
     xhtmlOut: false,
-    linkify: opts.discourse.features.linkify,
+    linkify: siteSettings.enable_markdown_linkify,
     typographer: siteSettings.enable_markdown_typographer
   });
 
+  opts.engine.linkify.tlds(siteSettings.markdown_linkify_tlds.split('|'));
+
   setupUrlDecoding(opts.engine);
   setupHoister(opts.engine);
   setupImageDimensions(opts.engine);