Current behavior

When no cores are installed, I would expect thatlistall returned all theexisting boards (like the Boards menu in the IDE). For a new user it's not clear that it only lists the boardswhose cores are installed, also becausecore install is documented in the README afterboard listall.

$ arduino-cli board listallBoard Name FQBN$ arduino-cli board[...]  listall     List all known boards and their corresponding FQBN.[...]

Suggested behavior

$ arduino-cli board listallNo known boards: install your first core with "arduino-cli core install <core>" to support its boards.$ arduino-cli board[...]  listall     List all known boards (and their corresponding FQBN) according to the installed cores.[...]

Also, would it be possible to add aboard search command to list all the existing boards (even if not installed)? Do we have such data around?
Most users think like this:I have a board ->I know its name but I don't know what core it requires ->Please install whatever core is needed for my board