Adding option to set global toggles.

[akowalik-transporeon]

This small change adds option to set some simple toggles in the global portion of haproxy configuration. This is needed for some smaller, one-of-a-kind fixes, like this one: FireBurn/haproxy@f1e82e9 where creating and maintaining a list would be very burdensome.

This could be achieved by misusing global tunes (just create a tune with empty value), but that approach looks like a really ugly hack.

[goldyfruit]

Thanks @akowalik-transporeon 👍