feat: add initial experimental Twitch Eventsub support (#5837)

Co-authored-by: nerix <nerixdev@outlook.de>

src/widgets/settingspages/AboutPage.cpp

@@ -129,6 +129,9 @@ AboutPage::AboutPage()
             addLicense(form.getElement(), "expected-lite",
                        "https://github.com/martinmoene/expected-lite",
                        ":/licenses/expected-lite.txt");
+            addLicense(form.getElement(), "Howard Hinnant's date.h",
+                       "https://github.com/HowardHinnant/date",
+                       ":/licenses/howard-hinnant-date.txt");
         }
 
         // Attributions

src/widgets/settingspages/GeneralPage.cpp

@@ -1273,6 +1273,10 @@ void GeneralPage::initLayout(GeneralPageView &layout)
                      "with sound playback on your system")
         ->addTo(layout);
 
+    layout.addCheckbox(
+        "Enable experimental Twitch EventSub support (requires restart)",
+        s.enableExperimentalEventSub);
+
     layout.addStretch();
 
     // invisible element for width