Replace Grape::Config by ActiveSupport::Configurable

[ericproulx]

This PR replaces Grape::Config::Configuration by ActiveSupport::Configurable. Same behavior is expected

[dblock]

What do you think about inheriting/extending Config from ActiveSupport::Configurable instead and keeping reset? It's a common pattern used in tests (you had to copy that code too here).

[ericproulx]

What do you think about inheriting/extending Config from ActiveSupport::Configurable instead and keeping reset? It's a common pattern used in tests (you had to copy that code too here).

The test wasn't actually testing the config part but the build_param_with options. I got rid of the around and use the option properly. I know it's a common practice in test to do the reset but it's only for testing not production. I tend to avoid functions that are just needed when testing.