feat: execute service as distributed erlang (#96)

To create a cluster with distributed nodes, the following changes were made:

* Use [`dns_cluster`][0] to execute distributed nodes
* Add _script_ to execute distributed nodes locally

Also, improve local execution by:

* Use [`mix release`][1] to make easier [deploy `phoenix`][2]
* Use [`compose watch`][3] to synchronize code from the host with the service

Some minor improvements:

* Ignore files and folders in git and docker
* Remove boilerplate comments

[0]: https://github.com/phoenixframework/dns_cluster
[1]: https://hexdocs.pm/mix/Mix.Tasks.Release.html
[2]: https://hexdocs.pm/phoenix/releases.html
[3]: https://docs.docker.com/compose/how-tos/file-watch/

Co-authored-by: Joao P Dubas <joao.dubas@gmail.com>
Reviewed-on: #96
Co-authored-by: Joao P Dubas <joao.dubas+gitea@gmail.com>
Co-committed-by: Joao P Dubas <joao.dubas+gitea@gmail.com>

lib/wabanex/release.ex

@@ -0,0 +1,28 @@
+defmodule Wabanex.Release do
+  @moduledoc """
+  Used for executing DB release tasks when run in production without Mix
+  installed.
+  """
+  @app :wabanex
+
+  def migrate do
+    load_app()
+
+    for repo <- repos() do
+      {:ok, _, _} = Ecto.Migrator.with_repo(repo, &Ecto.Migrator.run(&1, :up, all: true))
+    end
+  end
+
+  def rollback(repo, version) do
+    load_app()
+    {:ok, _, _} = Ecto.Migrator.with_repo(repo, &Ecto.Migrator.run(&1, :down, to: version))
+  end
+
+  defp repos do
+    Application.fetch_env!(@app, :ecto_repos)
+  end
+
+  defp load_app do
+    Application.load(@app)
+  end
+end