Add migration docs

docs/Migration-1.12.md

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+# Migration from 1.11.x to 1.12.x
+
+This guide contains instructions for migration from Wultra Mobile Token SDK for iOS version `1.11.x` to version `1.12.x`.
+
+## Implement status in WMTUserOperation
+
+### Added Functionality
+
+The following status property was added to the `WMTUserOperations`:
+
+```swift
+    /// Processing status of the operation
+    public let status: Status
+
+    /// Processing status of the operation
+    public enum Status: String, Codable, CaseIterable {
+        /// Operation was approved
+        case approved = "APPROVED"
+        /// Operation was rejected
+        case rejected = "REJECTED"
+        /// Operation is pending its resolution
+        case pending = "PENDING"
+        /// Operation was canceled
+        case canceled = "CANCELED"
+        /// Operation expired
+        case expired = "EXPIRED"
+        /// Operation failed
+        case failed = "FAILED"
+    }
+```
+
+The `WMTUserOperation.status` now represents the status of an operation, making the `WMTOperationHistoryEntry` redundant. As a result, `WMTOperationHistoryEntry` has been removed. In all instances where `WMTOperationHistoryEntry` was previously used, `WMTUserOperation` is used instead.
+
+### Replaced at
+
+In the `getHistory` method of `WMTOperations`, `WMTOperationHistoryEntry` has been replaced by `WMTUserOperation` for retrieving user operation history.
+
+```swift
+    /// Retrieves the history of user operations with its current status.
+    /// - Parameters:
+    ///   - authentication: Authentication object for signing.
+    ///   - completion: Result completion.
+    ///                 This completion is always called on the main thread.
+    /// - Returns: Operation object for its state observation.
+    @discardableResult
+    func getHistory(authentication: PowerAuthAuthentication, completion: @escaping(Result<[WMTUserOperation], WMTError>) -> Void) -> Operation?
+```