feat: add back button in navigation bar when navigating from communities to message author's DM

[VityaSchel]

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Description

I have added returnToConversation state property that has ReturnToConversationProps type. It is where information stored about where to navigate when user presses back button in navigation bar when returning from direct messages conversation with Community participant.

I have used existing BackButton component and openConversationToSpecificMessage function to navigate user exactly where they were before pressing avatar of some other user.

Also I handled cases like deleting returning conversation while in DMs (user navigates to someone's DM -> deletes community) and deleting current selected conversation while having return state (user navigated to someone's DM conversation -> deletes it) — in both cases returnToConversation is reset, hiding back button.

See #2595

[pottsandpans]

This will be tracked internally on Jira (SES-1940) for code review.``