feat: add untraced ctx method

[robertlaurin]

Support untraced usage in a non block structure open-telemetry/opentelemetry-ruby-contrib#965 (comment)

[robertlaurin]

Alternate considered is that we can instead amend the existing interface to support block structure or not depending if a block is provided.

      # Disables tracing within the provided block.
      def untraced
        if block_given?
          Context.with_value(UNTRACED_KEY, true) do |ctx, _|
            yield ctx
          end
        else
          Context.set_value(UNTRACED_KEY, true)
        end
      end

[fbogsany]

Can we modify untraced to take an optional context arg and optional block? I.e.

def untraced(context = Context.current)
  context = context.set_value(UNTRACED_KEY, true)
  if block_given?
    Context.with_current(context) { |ctx| yield ctx }
  else
    context
  end
end

[robertlaurin]

Updated

[fbogsany]

LGTM, once you've appeased the cop.