[feature] Add group actions

[lsdrfrx]

Explanation

Need to add handle_event macro to handle group events like joining/quitting group and TelegramEx.Builders.Group to perform group actions:

• Get group members
• Manage user permissions
• Kick/ban user
• Get banned users
• Pin messages
• Delete member message

Readiness criteria

• Added events handling via TelegramEx.Server and created new macro handle_event to add custom event handlers
• Created new builder TelegramEx.Builder.Group and it works correctly
• Added API docs into README.md
• Added demo usage into example/