Merge branch 'feature/group-chats' into 'development'

Docs/XXMessengerClient.md

Sources/XXClient/Callbacks/GroupChatProcessor.swift

...essengerClient/Messenger/Functions/MessengerDestroy.swift

...enger/Functions/MessengerRegisterGroupChatProcessor.swift

...nger/Functions/MessengerRegisterGroupRequestHandler.swift

...rClient/Messenger/Functions/MessengerStartGroupChat.swift

Sources/XXMessengerClient/Messenger/Messenger.swift

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

.../XXMessengerClient/Utils/GroupChatProcessorRegistry.swift

...MessengerClient/Utils/GroupRequestCallbacksRegistry.swift

Sources/XXMessengerClient/Utils/ListenersRegistry.swift

...ientTests/Messenger/Functions/MessengerDestroyTests.swift

.../Functions/MessengerRegisterGroupChatProcessorTests.swift

...Functions/MessengerRegisterGroupRequestHandlerTests.swift

...ts/Messenger/Functions/MessengerStartGroupChatTests.swift

Tests/XXMessengerClientTests/TestHelpers/TestDoubles.swift

...erClientTests/Utils/GroupChatProcessorRegistryTests.swift

...lientTests/Utils/GroupRequestCallbacksRegistryTests.swift