Include HTTP status code in AppNotFound exception

This PR preserves HTTP status code in the AppNotFound exception as it is e.g. already done in the Server exception. In some cases knowing the HTTP status code can give you more details on the problem, e.g. if not the app is the problem but the account/AuthData.

BTW: Java 11 for Kotlin seems to be too old, that doesn't work for me and in the GitLab pipeline, too. In my opinion Java 17 would be a good option. I use this config:

kotlin {
    jvmToolchain(17)
}

android {

    // ... some more lines skipped

    compileOptions {
        sourceCompatibility = JavaVersion.VERSION_17
        targetCompatibility = JavaVersion.VERSION_17
    }
    kotlin {
        compilerOptions {
            jvmTarget.set(JvmTarget.JVM_17)
        }
    }

@theimpulson Should I include that config in my PR?