Add zero-config self hosting on Render (#612)

* v1 of backend implementation for self hosting

* Add docs

* Add upgrades controller

* Add global helpers for self hosting mode

* Add self host settings controller

* Conditionally show self hosting settings

* Environment and config updates

* Complete upgrade prompting flow

* Update config for forked repo

* Move configuration of github provider within class

* Add upgrades cron

* Update deploy button

* Update guides

* Fix render deployer

* Typo

* Enable auto upgrades

* Fix cron

* Make upgrade modes more clear and consistent

* Trigger new available version

* Fix logic for displaying upgrade prompts

* Finish implementation

* Fix regression

* Trigger new version

* Add i18n translations

* trigger new version

* reduce caching time for testing

* Decrease cache for testing

* trigger upgrade

* trigger upgrade

* Only trigger deploy once

* trigger upgrade

* If target is commit, always upgrade if any upgrade is available

* trigger upgrade

* trigger upgrade

* Test release

* Change back to maybe repo for defaults

* Fix lint errors

* Clearer naming

* Fix relative link

* Add abs path

* Relative link

* Update docs

app/models/upgrader.rb

@@ -0,0 +1,57 @@
+class Upgrader
+  include Provided
+
+  class << self
+    attr_writer :config
+
+    def config
+      @config ||= Config.new
+    end
+
+    def upgrade_to(commit_or_upgrade)
+      upgrade = commit_or_upgrade.is_a?(String) ? find_upgrade(commit_or_upgrade) : commit_or_upgrade
+      config.deployer.deploy(upgrade)
+    end
+
+    def find_upgrade(commit)
+      upgrade_candidates.find { |candidate| candidate.commit_sha == commit }
+    end
+
+    def available_upgrade
+      available_upgrades.first
+    end
+
+    # Default to showing releases first, then commits
+    def completed_upgrade
+      completed_upgrades.find { |upgrade| upgrade.type == "release" } || completed_upgrades.first
+    end
+
+    def available_upgrade_by_type(type)
+      if type == "commit"
+        commit_upgrade = available_upgrades.find { |upgrade| upgrade.type == "commit" }
+        commit_upgrade || available_upgrades.first
+      elsif type == "release"
+        available_upgrades.find { |upgrade| upgrade.type == "release" }
+      end
+    end
+
+    private
+      def available_upgrades
+        upgrade_candidates.select(&:available?)
+      end
+
+      def completed_upgrades
+        upgrade_candidates.select(&:complete?)
+      end
+
+      def upgrade_candidates
+        latest_candidates = fetch_latest_upgrade_candidates_from_provider
+        return [] unless latest_candidates
+
+        commit_candidate = Upgrade.new("commit", latest_candidates[:commit])
+        release_candidate = latest_candidates[:release] && Upgrade.new("release", latest_candidates[:release])
+
+        [ release_candidate, commit_candidate ].compact.uniq { |candidate| candidate.commit_sha }
+      end
+  end
+end