avoid series of effects involved in start-public-chat if re-adding already active chat

[bitsikka]

Problem

If a user re-joins a public chat that she already joined, currently the process of series of effects involved in starting a fresh public chat is triggered unnecessarily. Instead the app should avoid it by simply navigating to the already active chat.

While, on the surface, this does not change anything for users in general, once PR #7454 is merged, not having this will cause visual inconsistency of showing loading intro header meaninglessly.

This should also make re-addition and navigation to of already active chat tad bit faster.

Implementation

when adding/joining/re-adding public chat, check if the chat topic is already active and navigate to it instead of going through the whole creating the chat process.

Notes

As a general optimization, this implementation approach is also good to make use of in other points in the app where new chat creation is triggered (e.g. from DApp).

Future Steps

Implement the same approach to per DApp public chat, and any other areas that creates new chat.