Use option to set default timeout

[gadenbuie]

Setting the default timeout currently requires the following code:

chrome <- chromote::default_chromote_object()
chrome$default_timeout <- 60
chromote::set_default_chromote_object(chrome)

b <- ChromoteSession$new()
b$default_timeout
#> 60

It'd be helpful to have an option, e.g. chromote.timeout (exists and is used for connection and setup timeouts) or chromote.timeout.default if we want to separate the two options.