Default terminal.integrated.detectLocale to "on"

[testlabauto]

(from discussion: #11012)

We should make:

terminal.integrated.detectLocale set to "on" a positron default to avoid cross platform confusion for users.

Test code (R) that can fail on OSX:

stringi::stri_locale_get()
#> [1] "en_US_POSIX"

We would like users to always see:

stringi::stri_locale_get()
#> [1] "en_US"

Regardless of the operating system.