Merge branch 'feature/messenger-backup' into 'development'

Docs/XXMessengerClient.md

...gerClient/Messenger/Functions/MessengerBackupParams.swift

...Client/Messenger/Functions/MessengerIsBackupRunning.swift

...Messenger/Functions/MessengerRegisterBackupCallback.swift

...erClient/Messenger/Functions/MessengerRestoreBackup.swift

...gerClient/Messenger/Functions/MessengerResumeBackup.swift

...ngerClient/Messenger/Functions/MessengerStartBackup.swift

...engerClient/Messenger/Functions/MessengerStopBackup.swift

Sources/XXMessengerClient/Messenger/Messenger.swift

...es/XXMessengerClient/Messenger/MessengerEnvironment.swift

Sources/XXMessengerClient/Utils/BackupCallbackRegistry.swift

Sources/XXMessengerClient/Utils/BackupParams.swift

...ests/Messenger/Functions/MessengerBackupParamsTests.swift

...s/Messenger/Functions/MessengerIsBackupRunningTests.swift

...nger/Functions/MessengerRegisterBackupCallbackTests.swift

...ests/Messenger/Functions/MessengerResumeBackupTests.swift

...Tests/Messenger/Functions/MessengerStartBackupTests.swift

...tTests/Messenger/Functions/MessengerStopBackupTests.swift

Tests/XXMessengerClientTests/TestHelpers/StringData.swift

Tests/XXMessengerClientTests/TestHelpers/TestDoubles.swift