Merge branch 'consistent-snippet-prefix' into 'master'

Use $ as the snippet prefix so it's consistent

## What does this MR do?

Change like `Snippet #20073` to `Snippet $20073`

## Are there points in the code the reviewer needs to double check?

Are there any other places need this change?

See merge request !4338

app/views/shared/snippets/_header.html.haml

@@ -4,7 +4,7 @@
       = visibility_level_label(@snippet.visibility_level)
     = visibility_level_icon(@snippet.visibility_level, fw: false)
   %strong.item-title
-    Snippet ##{@snippet.id}
+    Snippet $#{@snippet.id}
   %span.creator
     created by #{link_to_member(@project, @snippet.author, size: 24, author_class: "author item-title")}
     = time_ago_with_tooltip(@snippet.created_at, placement: 'bottom', html_class: 'snippet_updated_ago')