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/config.rb

@@ -0,0 +1,17 @@
+class Upgrader::Config
+  attr_reader :env, :options
+
+  def initialize(options = {}, env: ENV)
+    @env = env
+    @options = options
+  end
+
+  def deployer
+    factory = Upgrader::Deployer
+    factory.for(hosting_platform)
+  end
+
+  def hosting_platform
+    options[:hosting_platform] || env["HOSTING_PLATFORM"]
+  end
+end