Add a way to stream logs during the diagnose subcommand

[ahoppen]

The OS Log store often doesn’t contain all log entries at lower log levels anymore. I think it would be interesting to start the diagnose subcommand with a prompt asking the user to reproduce the issue while we run log stream --predicate 'subsystem CONTAINS "sourcekit-lsp"' --source --level debug.

While doing this, we might also consider adding --source to the command with which we get the previous OSLog entries.

rdar://126622964