feat: Include details for web api errors

fixes: slack-ruby#482

Currently when we get the error message we get no details of what went
wrong unless we get the response_metadata for the error which is not
intuitive as most people when they get an error and print the exception
they would expect to see as much details as possible.

Additionally updated ruby-version in the project to be the latest as
most people would be using that one as their default, though not
changing the one required by the gem

.ruby-version

@@ -1 +1 @@
-2.7.6
+3.2.0

lib/slack/web/api/errors/slack_error.rb

@@ -22,6 +22,12 @@ def errors
           def response_metadata
             response.body.response_metadata
           end
+
+          def to_s
+            errors_message = ", errors=#{errors}" unless errors.nil?
+            response_metadata_message = ", response_metadata=#{response_metadata}" unless response_metadata.nil?
+            "#{error}#{errors_message || ''}#{response_metadata_message || ''}"
+          end
         end
       end
     end

spec/slack/web/api/errors/slack_error_spec.rb

@@ -21,7 +21,7 @@
   rescue described_class => e
     expect(e.response).not_to be_nil
     expect(e.response.status).to eq 200
-    expect(e.message).to eql 'invalid_arguments'
+    expect(e.message).to eql "invalid_arguments, response_metadata=#{e.response_metadata}"
     expect(e.error).to eql 'invalid_arguments'
     expect(e.response_metadata).to eq(
       'messages' => [