feat(backend/shared): save all messages in ai chat to db bb-454

[marharita08]

Summary

#454 save all messages in ai chat to db.

Added

• migations to add chat_messages to db
• entity, model, repository and service for chat messages

Updated

• ai assistant service to use chat messages service to save messages to db
• ai assistant helpers to return messages in ChatMessageCreateDto type
• request and response types of ai assistant endpoints
• chat.slice.ts to add chat history to the state
• some components of chat to send text messages to backend, which should be saved to db

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