Moved urls redirects (#4342)

Generate redirect for /latest/ on moved URLs

app/_plugins/generators/alias_generator.rb

@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require 'yaml'
 # Alias Generator for Posts using Netlify _redirects
 #
 # Generates redirect pages for posts with aliases set in the YAML Front Matter.
@@ -33,10 +34,15 @@ class AliasGenerator < Generator
     def generate(site) # rubocop:disable Metrics/AbcSize
       @redirects = []
 
+      # Generate redirect_to from frontmatter redirects
       site.pages.each do |page|
         generate_aliases(page.destination('').gsub(/index\.(html|htm)$/, ''), page)
       end
 
+      # Generate redirects from moved_urls
+      moved_pages = YAML.load_file("#{__dir__}/../../moved_urls.yml")
+      generate_moved_aliases(moved_pages)
+
       # Read existing _redirects file
       existing = "#{File.read("#{__dir__}/../../_redirects")}\n"
 
@@ -47,6 +53,14 @@ def generate(site) # rubocop:disable Metrics/AbcSize
       site.pages << page
     end
 
+    def generate_moved_aliases(moved_pages)
+      moved_pages.each do |k,v|
+        k = k.sub("/VERSION/", "/latest/")
+        v = v.sub("/VERSION/", "/latest/")
+        @redirects.push("#{k}\t#{v}")
+      end
+    end
+
     def generate_aliases(_destination_path, page) # rubocop:disable Metrics/MethodLength
       aliases = page.data['alias']
       alias_paths ||= []