Add config/tokens.yml template
Remove secret_token.rb
Load secret_key_base from tokens.yml, fallback to config.secret_key_base
Replace config.secret_key_base with secrets.secret_key_base in test
Add test for custom tokens stored in config/tokens.yml
Rename tokens.yml to secrets.yml
Add comment about secret_key_base in secrets.yml
Merge pull request #13298 from rails/secret_tokens

Create config/secrets.yml file for store of tokens