[Housekeeping] Refactor settings model (#165)

* [WIP] renamed current settings module and tables to have backup suffix

* Created new settings table, schema, and context

* Migrated from old settings module to new one

* Removed settings backup modules

* Added some tests and docs

priv/repo/migrations/20240404172256_rename_settings_table.exs

@@ -0,0 +1,7 @@
+defmodule Pinchflat.Repo.Migrations.RenameSettingsTable do
+  use Ecto.Migration
+
+  def change do
+    rename table(:settings), to: table(:settings_backup)
+  end
+end