Libs(Ruby): add a kitchen sink test

This test is like the others added across our other libs. It walks
through some light API interactions just to check how the serialization
is working WRT nullable containers and empty response bodies.

Setting `SVIX_TOKEN` and `SVIX_SERVER_URL` env vars will optionally
enable the test which is skipped otherwise.

ruby/spec/kitchen_sink_spec.rb

@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+require_relative "../lib/svix"
+
+token = ENV["SVIX_TOKEN"]
+server_url = ENV["SVIX_SERVER_URL"]
+test_client = nil
+
+if token.nil? || server_url.nil?
+  warn("Unable to instantiate test client without both `SVIX_TOKEN` and `SVIX_SERVER_URL`")
+else
+  opts = Svix::SvixOptions.new(false, server_url)
+  test_client = Svix::Client.new(token, opts)
+end
+
+RSpec.describe Svix::Client do
+  describe "Endpoint CRUD", :if => !test_client.nil? do
+    it "seems to work okay" do
+      app = test_client.application.create(Svix::ApplicationIn.new(name: "App"))
+
+      begin
+        test_client.event_type.create(Svix::EventTypeIn.new(name: "event.started", description: "Something started"))
+      rescue Svix::ApiError => err
+        # Conflicts are expected from test run to test run, but other statuses are not.
+        expect(err.code).to eq(409)
+      end
+      begin
+        test_client.event_type.create(Svix::EventTypeIn.new(name: "event.ended", description: "Something ended"))
+      rescue Svix::ApiError => err
+        # Conflicts are expected from test run to test run, but other statuses are not.
+        expect(err.code).to eq(409)
+      end
+
+      ep = test_client.endpoint.create(
+        app.id,
+        Svix::EndpointIn.new(url: "https://example.svix.com/", channels: %w[ch0 ch1])
+      )
+
+      expect(ep.channels.to_set).to eq(%w[ch0 ch1].to_set)
+      expect(ep.filter_types).to be_nil
+
+      ep_patched = test_client.endpoint.patch(app.id, ep.id, Svix::EndpointPatch.new(filter_types: %w[event.started event.ended]))
+
+      expect(ep_patched.channels.to_set).to eq(%w[ch0 ch1].to_set)
+      expect(ep_patched.filter_types.to_set).to eq(%w[event.started event.ended].to_set)
+
+      # If the serialization is handling empty response bodies, this should not throw an exception
+      test_client.endpoint.delete(app.id, ep.id)
+    end
+  end
+end