Encrypt API tokens (#2360)

Store API tokens encrypted in the database.

During the database migration a randomly generated key will be used encrypt the tokens if no ENCRYPTION_KEY environment variable was provided.

If the application is started without the presence of an ENCRYPTION_KEY (or if the key failed to decrypt the existing tokens), the UI will display a warning with further instructions.

mix.exs

@@ -60,7 +60,8 @@ defmodule TeslaMate.MixProject do
       {:timex, "~> 3.0"},
       {:tortoise, "~> 0.10"},
       {:tzdata, "~> 1.1"},
-      {:websockex, "~> 0.4"}
+      {:websockex, "~> 0.4"},
+      {:cloak_ecto, "~> 1.2"}
     ]
   end