Automatic discovery of the sliding sync proxy. (#535)

* Automatic discovery of the sliding sync proxy.

* Handle homeserver detection from a MXID.

* Update sliding sync info link, SDK and bump patch.

Add a migration on the new version. The change in restoration token format requires the user to sign in again, but this will fail with the existing device ID.

ElementX/Sources/Application/AppCoordinator.swift

@@ -136,9 +136,10 @@ class AppCoordinator: AppCoordinatorProtocol {
     private func performMigrationsIfNecessary(from oldVersion: Version, to newVersion: Version) {
         guard oldVersion != newVersion else { return }
         
-        if oldVersion < Version(1, 0, 17) {
-            // Version 1.0.17 hardcoded a new sliding sync proxy for matrix.org
-            // Force a sign out for the user to log in with the new proxy.
+        if oldVersion < Version(1, 0, 20) {
+            // Version 1.0.20 introduced a new format for restoration tokens.
+            // Remove user data to prevent conflict in the crypto store
+            // with the newly generated device ID when signing in again.
             MXLog.warning("Clearing user data for hardcoded proxy.")
             wipeUserData()
         }

ElementX/Sources/Application/AppSettings.swift

@@ -24,7 +24,6 @@ final class AppSettings: ObservableObject {
         case timelineStyle
         case enableAnalytics
         case isIdentifiedForAnalytics
-        case slidingSyncProxyBaseURLString
         case enableInAppNotifications
         case pusherProfileTag
     }
@@ -62,7 +61,12 @@ final class AppSettings: ObservableObject {
     
     /// An override of the homeserver's Sliding Sync proxy URL. This allows development against servers
     /// that don't yet have an officially trusted proxy configured in their well-known.
-    let slidingSyncProxyURL = URL(staticString: "https://slidingsync.lab.matrix.org")
+    let slidingSyncProxyURL: URL? = nil
+    
+    // MARK: - Authentication
+    
+    /// The URL that is opened when tapping the Learn more button on the sliding sync alert during authentication.
+    let slidingSyncLearnMoreURL = URL(staticString: "https://github.com/matrix-org/sliding-sync/blob/main/docs/Landing.md")
     
     // MARK: - Notifications