[doc] locale is missing from the CLI config spec

[kittaakos]

Describe the problem

locale is a valid CLI config entry, but it's undocumented yet. https://arduino.github.io/arduino-cli/0.27/configuration/#configuration-keys

To reproduce

Go to https://arduino.github.io/arduino-cli/0.27/configuration/#configuration-keys, locale is not there.

Expected behavior

locale is documented

Arduino CLI version

It's not a CLI malfunction

Operating system

macOS

Operating system version

12.5.1

Additional context

No response

Issue checklist

• I searched for previous reports in the issue tracker
• I verified the problem still occurs when using the nightly build
• My report contains all necessary details

[per1234]

Beyond a documentation deficiency, the configuration key is not even supported by the arduino-cli config command:

$ arduino-cli version
arduino-cli.exe  Version: git-snapshot Commit: 54a0bc07 Date: 2022-10-18T10:28:55Z

$ arduino-cli config set locale de
Settings key doesn't exist

I think that bug should be fixed before or during the documentation update since the user will expect to have full functionality from any documented configuration key.