Reduce env read duplication in config hierarchy

config/config.exs

@@ -12,8 +12,8 @@ config :gc_index_relay,
   generators: [timestamp_type: :utc_datetime]
 
 config :gc_index_relay, GcIndexRelay.Repo,
-  username: System.get_env("POSTGRES_ADMIN_USER"),
-  password: System.get_env("POSTGRES_ADMIN_PASSWORD"),
+  username: System.get_env("POSTGRES_USER"),
+  password: System.get_env("POSTGRES_PASSWORD"),
   database: System.get_env("POSTGRES_DB"),
   hostname: System.get_env("POSTGRES_HOST"),
   stacktrace: true,

config/dev.exs

@@ -2,11 +2,8 @@ import Config
 
 # Configure your database
 config :gc_index_relay, GcIndexRelay.Repo,
-  username: System.get_env("POSTGRES_USER"),
-  password: System.get_env("POSTGRES_PASSWORD"),
-  database: System.get_env("POSTGRES_DB"),
-  hostname: System.get_env("POSTGRES_HOST"),
-  port: System.get_env("POSTGRES_PORT"),
+  username: System.get_env("POSTGRES_ADMIN_USER"),
+  password: System.get_env("POSTGRES_ADMIN_PASSWORD"),
   stacktrace: true,
   show_sensitive_data_on_connection_error: true,
   pool_size: 10

config/test.exs

@@ -10,8 +10,6 @@ config :gc_index_relay, :start_repo, true
 config :gc_index_relay, GcIndexRelay.Repo,
   username: System.get_env("POSTGRES_USER"),
   password: System.get_env("POSTGRES_PASSWORD"),
-  hostname: System.get_env("POSTGRES_HOST"),
-  port: System.get_env("POSTGRES_PORT"),
   database: "#{System.get_env("POSTGRES_DB")}#{System.get_env("MIX_TEST_PARTITION")}",
   pool: Ecto.Adapters.SQL.Sandbox,
   pool_size: System.schedulers_online() * 2