feat: remove `secrets.yml` in favor of `app.yml` #1530

Job	Run time
audit_dependencies	5s
rubocop	7s
test	9s
test_generated_apps (defaults, ackama_rails_template.config.yml, yes)	4m 17s
test_generated_apps (all, ci/configs/all.yml, yes)	5m 44s
test_generated_apps (all-typescript, ci/configs/all-typescript.yml, yes)	6m 35s
test_generated_apps (basic, ci/configs/basic.yml)	3m 48s
test_generated_apps (basic-typescript, ci/configs/basic-typescript.yml)	4m 16s
test_generated_apps (github_actions, ci/configs/github_actions.yml, yes)	3m 45s
test_generated_apps (react, ci/configs/react.yml)	4m 15s
test_generated_apps (react-typescript, ci/configs/react-typescript.yml)	5m 10s
test_generated_apps (sidekiq, ci/configs/sidekiq.yml)	3m 47s
test_generated_apps (devise, ci/configs/devise.yml)	4m 49s
test_generated_apps (basic_with_skips, ci/configs/basic.yml, --skip-spring --skip-javascript)	3m 42s
test_generated_apps (bootstrap, ci/configs/bootstrap.yml)	4m 19s
test_generated_apps (bootstrap-typescript, ci/configs/bootstrap-typescript.yml)	4m 32s
test_generated_apps (capistrano, ci/configs/deploy_with_capistrano.yml)	4m 0s
test_generated_apps (ackama_ec2_capistrano, ci/configs/deploy_with_ackama_ec2_capistrano.yml)	4m 7s
	1h 7m 27s

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