chore(config): Deprecate & warn for `--global` (`--location=global`)

[darcyclarke]

[fritzy]

npm/cli#4878

[mscdex]

Why was the cli -g/--global flag deprecated (in npm/cli#4879 and especially within the same major version as this seems pretty breaking IMO)? Having to do --location=global seems overly verbose.

[darcyclarke]

@mscdex deprecation does not mean removal (so npm i -g <pkg> still works the same way). We're intending to patch this. Going to close this issue & make a new one explaining the details further there (will cross link once it's up)