Update operations dry-monads support

[cllns]

Right now the generated spec/support/operations.rb file (from #23) is:

require "dry/monads"

RSpec.configure do |config|
  # Provide `Success` and `Failure` for testing operation results
  config.include Dry::Monads[:result]
end

But now with the Dry::Monad's RSpec extension (PR: dry-rb/dry-monads#183) we don't need to do that anymore. Instead, we can just do Dry::Monads.load_extensions(:rspec). This also has a huge advantage of allowing expect(result).to be_a(Success) whereas before you could only specify a specific Success object, e.g. Success(123). See: dry-rb/dry-monads#182 for more on that issue.

So now, based on my testing, we can update that file to just:

Dry::Monads.load_extensions(:rspec)

However, it seems like overkill to create a file for just 1 line. In the name of pragmatism, I'd just include that directly in spec/spec_helper.rb. Or, ideally, we could change dry-monads behavior to automatically load the :rspec extension when it's bundled with rspec. What are your thoughts on doing that @flash-gordon? cc @timriley

[flash-gordon]

@cllns can we maybe generalize it with spec/extensions or something similar? I prefer avoiding doing things automatically when unexpected side effects can occur. In this particular case, my gut feeling tells me these can happen. I want it to be an opt-in behavior from the dry-monads' POV.
While I was writing this, another idea came to mind. dry-monads could autoload the rspec ext by default, but issue a warning that can be silenced. Hanami could silence it by default.
Some non-Hanami users may have issues with the loading order. Of course, they are not likely in the case of rspec; rspec will load first in 99% of cases.
These are my first thoughts