add an option to deactivate chrome echo_cmd

[Christophe Dervieux]

I think this is not required in all case and it would allow to deactivate echoing during test.

We are talking about this

crrri/R/Chrome.R

Line 258 in 9337a19

 tryCatch(processx::process$new(bin, chrome_args, echo_cmd = TRUE), 

and not use TRUE but getOption("crrri.echo_cmd", TRUE) or a more generic crrri.verbose option.