Messages: Add 'copy to clipboard' button for key,value,headers

[Haarolean]

Currently, we have a 'copy to clipboard' button for the overall message, which copies the contents as a JSON.

TODO:

• Add a button for copying the key, value, and headers (one button per tab)

[svrmnk]

I'd like to work on this! Can you please clarify, the task is to add 3 buttons?

[Haarolean]

@svrmnk hi, we still don't have the design for this ready yet. Feel free to pick any other one from "up for grabs" board.