Use static sitemaps, generated locally (#4323)

Adds 

- `/public/sitemap.txt`
- `/public/sitemap.xml.gz`

Because generating each of them is time expensive, but doesn't change
very often
We can re-generate them often in local dev environments and re-push them

For now, to re-generate them locally, the manual steps are:
From repo root, with a clean git status…

```sh
git pull main
git checkout -b update_static_sitemap
rm public/sitemap.*
bundle exec rails server 
curl -o public/sitemap.txt https://crimethinc.com/sitemap_txt
curl -o public/sitemap.xml https://crimethinc.com/sitemap_xml
gzip --force --best public/sitemap.xml
git add .
git commit -am "Update static sitemaps $(date)"
git push
```

Author: veganstraightedge

app/controllers/sitemap_controller.rb

@@ -22,7 +22,14 @@ class SitemapController < ApplicationController
     %w[czech deutsch polski slovenscina slovensko]
   ].flatten.freeze
 
-  def show
+  before_action :set_all_data
+
+  def sitemap_xml;  end
+  def sitemap_text; end
+
+  private
+
+  def set_all_data
     set_latest_article
     set_last_modified
 
@@ -87,8 +94,6 @@ def show
     set_episodes_last_modified
   end
 
-  private
-
   def set_latest_article
     @latest_article = Article.published.english.first
   end

app/middlewares/rack/redirect.rb

@@ -12,6 +12,7 @@ def call env
 
       # special case: non-ASCII paths
       redirects = {
+        '/sitemap.xml'    => '/sitemap.xml.gz',
         '/search?utf8=✓&' => '/search',
         '/tce/%uFEFF'     => '/tce'
       }

app/views/sitemap/show.text.erb app/views/sitemap/sitemap_txt.text.erb

@@ -4,8 +4,8 @@
   # sitemaps
   # xml: for robots/search engines
   # txt: for humans/archivers
-  get 'sitemap.xml', to: 'sitemap#show', defaults: { format: 'xml' }, as: :sitemap
-  get 'sitemap.txt', to: 'sitemap#show', defaults: { format: 'txt' }, as: :sitemap_txt
+  get 'sitemap_xml', to: 'sitemap#sitemap_xml', defaults: { format: 'xml' }, as: :sitemap_xml
+  get 'sitemap_txt', to: 'sitemap#sitemap_txt', defaults: { format: 'txt' }, as: :sitemap_txt
 
   # TODO: After switching the site auth to Devise, enable this auth protected route
   # # Sidekiq admin interface to monitor background jobs