chore: add dotenv

Gemfile.lock

@@ -82,6 +82,10 @@ GEM
     database_cleaner (1.7.0)
     deep_merge (1.2.1)
     diff-lcs (1.3)
+    dotenv (2.7.6)
+    dotenv-rails (2.7.6)
+      dotenv (= 2.7.6)
+      railties (>= 3.2)
     dynamic_form (1.1.4)
     encrypto_signo (1.0.0)
     erubi (1.10.0)
@@ -256,6 +260,7 @@ DEPENDENCIES
   clockwork
   coffee-rails (~> 4.2)
   database_cleaner
+  dotenv-rails
   dynamic_form
   encrypto_signo
   factory_bot_rails (~> 4.0)