Rails credentials read prevents Flipper from working on Rails < 5.2

[clinejj]

In https://github.com/flippercloud/flipper/pull/782, there was an update to read values from Rails credentials. Credentials were added in Rails 5.2, which means this throws an error when using Flipper 1.1.0+ and Rails < 5.2:

2.544 NoMethodError: undefined method `credentials' for #<Website::Application:0x0000ffff8676ff30>
2.544 /website/config/environment.rb:5:in `<top (required)>'
2.544 /usr/local/ruby-2.7.8/bin/bundle:23:in `load'
2.544 /usr/local/ruby-2.7.8/bin/bundle:23:in `<main>'
2.544 Tasks: TOP => environment
2.544 (See full trace by running task with --trace)

There isn't an explicit dependency on particular Rails versions in the gemspec, however flipper-active_record does have a requirement for Rails >= 4.2. Without getting too nitpicky on the solutions here, some possible options:

• Set a minimum Rails version in order to use Flipper
• Update the calls at https://github.com/flippercloud/flipper/blob/0e996298dec5f05d4a9feb11369cb7db4e402a09/lib/flipper/engine.rb#L41-L42 to check if the credentials method exists, and if not rely on the env vars

There's also a question of whether those env var checks need to happen there, rather than inside the cloud? block since they seem to only apply to cloud users (this is not used in a cloud application FWIW).

[jnunemaker]

Generally I’d say we don’t support versions that are EOL by rails but checking if the app responds to credentials seems easy. Any interest in a PR?

[clinejj]

Sounds good, will submit in the next week-ish