fix https://github.com/brave/brave-browser/issues/25789
Initially vpn state was per-profile.
However, we decided to share vpn state between all profiles.
With this change, one profile can have same vpn status if other
profile is purchased user.
So far vpn service manages two states.
The one is purchased state and the other is connection state.
Purchased state is still per-profile because skus service is per profile.
Although purchased state is managed by each profile,
same state is shared for all profiles eventually because skus service's
internal data is global.
In this PR connection state managing is moved from per-profile vpn service
to BraveVPNOSConnectionAPI global instance. Before this PR,
BraveVPNOSConnectionAPI didn't have state and only provided abstract interface
for os dependent vpn command such as connect or disconnect.
In the os system, there is only one connection state.
So, connection state also should be managed globally.
With that each profile can see same connection state.
Simon Hong
8dbfe025a1