Cached Network Image for Chat background

[Tanujkarteek]

As of now the background image for the chat UI is an Network Image but it would be better if we can use the CachedNetworkImage for the same or an image from local assets dir fetching it every time from the network is a tedious and overburdened step you can look into this, this is a very minute change, If you want I can create a PR with changes I have suggested