Introduce a build setting to detect Nightly builds. (#5852)

* Allow the AppIconBanner tool to be called with purely the build number.

And use that for the Element Pro Nightly.

* Use a build setting to determine Nightly builds.

ElementX/Sources/Application/Settings/AppSettings.swift

@@ -40,11 +40,10 @@ nonisolated enum AppBuildType {
         #if DEBUG
         return .debug
         #else
-        switch InfoPlistReader.main.baseBundleIdentifier {
-        case "io.element.elementx.nightly":
-            return .nightly
-        default:
-            return .release
+        if InfoPlistReader.main.isNightlyBuild {
+            .nightly
+        } else {
+            .release
         }
         #endif
     }