Merge branch 'main' into glitch-soc/merge-upstream

- `.env.production.sample`:
  Our sample config file is very different from upstream since it is much more
  complete. Upstream added documentation for a few env variables.
  Copied the new variables/documentation from upstream.
- `app/lib/feed_manager.rb`:
  Upstream added a timeline type (hashtags), while glitch-soc already had an
  extra one (direct messages). Not really a conflict but textually close
  changes.
  Ported upstream's changes.
- `app/models/custom_emoji.rb`:
  Upstream upped the custom emoji size limit, while glitch-soc had configurable
  limits.
  Upped the default limits accordingly.
- `streaming/index.js`:
  Upstream reworked how hastags were normalized. Minor conflict due to
  glitch-soc's handling of instance-local posts.
  Ported upstream's changes.

config/routes.rb

@@ -554,6 +554,15 @@ Rails.application.routes.draw do
         resource :note, only: :create, controller: 'accounts/notes'
       end
 
+      resources :tags, only: [:show], constraints: { id: /#{Tag::HASHTAG_NAME_RE}/ } do
+        member do
+          post :follow
+          post :unfollow
+        end
+      end
+
+      resources :followed_tags, only: [:index]
+
       resources :lists, only: [:index, :create, :show, :update, :destroy] do
         resource :accounts, only: [:show, :create, :destroy], controller: 'lists/accounts'
       end