Verbose mode

[rok-cesnovar]

I think it would make sense to have something like a verbose mode that could be used for troubleshooting, debugging, and developing with cmdstanr. I think an option would be just fine. This is not something a regular user would need.
Like

options("cmdstanr_verbose"= TRUE)

would print all commands and all output from processx. This came up when debugging a problem with @yizhang-yiz here

[jgabry]

That seems like a good idea