This change replaces
usage of `reqwest` and `hyper-util`
with custom connection establishment code
so it is done in the same way
as for IMAP and SMTP connections.
This way we control HTTP, IMAP and SMTP
connection establishment
and schedule connection attempts
to resolved IP addresses
in the same way for all 3 protocols.
Notification server uses APNS server
for heartbeat notifications,
so registering FCM tokens there
will result in failing to notify them
and unregistering them anyway.
