Add WebDAV backup and restore functionality

Introduces a new BackupActivity for configuration backup and restore, supporting both local storage and WebDAV servers. Adds WebDavManager and WebDavConfig for handling WebDAV operations, updates the navigation drawer and menu, and refactors AboutActivity to remove backup/restore logic. Includes new layouts and string resources for backup options and WebDAV settings.

V2rayNG/app/build.gradle.kts

@@ -158,6 +158,7 @@ dependencies {
     // Data and Storage Libraries
     implementation(libs.mmkv.static)
     implementation(libs.gson)
+    implementation(libs.okhttp)
 
     // Reactive and Utility Libraries
     implementation(libs.kotlinx.coroutines.android)