feat: add function returning all keys from store

Sources/UserDefaultsStore/UserDefaultsStore.swift

@@ -106,6 +106,14 @@ public struct UserDefaultsStore: UserDefaultsStoreProtocol {
     }
 
     // MARK: - Data Management
+
+    /// Returns all keys which are present in the store.
+    ///
+    /// - Returns: The array of  `String` representing all keys from the store.
+    public func keys() -> [String] {
+        let keys = userDefaults.dictionaryRepresentation().keys
+        return [String](keys)
+    }
 
     /// Removes the value associated with a given key.
     ///

Tests/UserDefaultsStoreTests/UserDefaultsStoreTests.swift

@@ -97,6 +97,26 @@ final class UserDefaultsStoreTests: XCTestCase {
         XCTAssertTrue(storageValue.isEmpty)
     }
 
+    /// Tests retrieving array containing all keys of the store
+    func testKeys() throws {
+        let store = createStore()
+
+        let value1 = "foo"
+        let key1 = "KEY_1"
+        store.set(value1, forKey: key1)
+
+        let value2 = "bar"
+        let key2 = "KEY_2"
+        store.set(value2, forKey: key2)
+
+        let keys = store.keys()
+        XCTAssertTrue(keys.contains(key1))
+        XCTAssertTrue(keys.contains(key2))
+
+        let key3 = "KEY_3"
+        XCTAssertFalse(keys.contains(key3))
+    }
+
     /// Tests removing a specific key-value pair.
     func testRemove() throws {
         let store = createStore()