feat: properly set OkHttp header (#2463)

properly send `User-Agent` and `Accept-Language` to `updateJson` server,
module developers can check `User-Agent` whether to send update to user
and set user preferred language for changelog.

also added cache to reduce update server load

manager/app/src/main/java/com/rifsxd/ksunext/KernelSUApplication.kt

@@ -6,12 +6,25 @@ import coil.Coil
 import coil.ImageLoader
 import me.zhanghai.android.appiconloader.coil.AppIconFetcher
 import me.zhanghai.android.appiconloader.coil.AppIconKeyer
+import okhttp3.Cache
+import okhttp3.OkHttpClient
 import java.io.File
+import java.util.Locale
 
 lateinit var ksuApp: KernelSUApplication
 
 class KernelSUApplication : Application() {
 
+    val okhttpClient =
+        OkHttpClient.Builder().cache(Cache(File(cacheDir, "okhttp"), 10 * 1024 * 1024))
+            .addInterceptor { block ->
+                block.proceed(
+                    block.request().newBuilder()
+                        .header("User-Agent", "KernelSU/${BuildConfig.VERSION_CODE}")
+                        .header("Accept-Language", Locale.getDefault().toLanguageTag()).build()
+                )
+            }.build()
+
     override fun onCreate() {
         super.onCreate()
         ksuApp = this