[Housekeeping] Reduce Docker image size (#231)

* First pass at cutting down image size

* Made selfhosted docker work multiplatform

* Updated compile-time value to be runtime

* Fixed issue with tzdata file permissions

* Applied better fix for tz issue

config/prod.exs

@@ -7,6 +7,8 @@ import Config
 # before starting your production server.
 config :pinchflat, PinchflatWeb.Endpoint, cache_static_manifest: "priv/static/cache_manifest.json"
 
+config :tzdata, :data_dir, "/etc/elixir_tzdata_data"
+
 # Configures Swoosh API Client
 config :swoosh, api_client: Swoosh.ApiClient.Finch, finch_name: Pinchflat.Finch