Bump minimum Elixir version to 1.10

With the release of Elixir 1.14, Elixir 1.9 is now end-of-life.

Elixir 1.10 Release Notes:
https://github.com/elixir-lang/elixir/releases/tag/v1.10.0

priv/templates/sample_config.eex

@@ -3,11 +3,7 @@
 # NOTE: This file should not be committed to a repo or otherwise made public
 # without removing sensitive information.
 
-<%= if Code.ensure_loaded?(Config) or not Code.ensure_loaded?(Mix.Config) do
-  "import Config"
-else
-  "use Mix.Config"
-end %>
+import Config
 
 config :pleroma, Pleroma.Web.Endpoint,
    url: [host: "<%= domain %>", scheme: "https", port: <%= port %>],