Merge branch 'feature/messenger-send-receive' into 'development'

Docs/XXMessengerClient.md

...ient/Messenger/Functions/MessengerListenForMessages.swift

...essenger/Functions/MessengerRegisterMessageListener.swift

...ngerClient/Messenger/Functions/MessengerSendMessage.swift

Sources/XXMessengerClient/Messenger/Messenger.swift

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

Sources/XXMessengerClient/Utils/AuthCallbacksRegistry.swift

Sources/XXMessengerClient/Utils/ListenersRegistry.swift

...Messenger/Functions/MessengerListenForMessagesTests.swift

...enger/Functions/MessengerRegisterAuthCallbacksTests.swift

...ger/Functions/MessengerRegisterMessageListenerTests.swift

...Tests/Messenger/Functions/MessengerSendMessageTests.swift

Tests/XXMessengerClientTests/TestHelpers/Message+stubs.swift

...ssengerClientTests/Utils/AuthCallbacksRegistryTests.swift

...XXMessengerClientTests/Utils/ListenersRegistryTests.swift