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/Services/BugReport/BugReportService.swift

@@ -88,7 +88,7 @@ class BugReportService: NSObject, BugReportServiceProtocol {
         
         params.append(contentsOf: defaultParams)
         
-        if InfoPlistReader.main.baseBundleIdentifier == "io.element.elementx.nightly" {
+        if AppBuildType.current == .nightly {
             bugReport.githubLabels.append("Nightly")
         }