feat: replace reqwest with hyper

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.

src/push.rs

@@ -61,16 +61,13 @@ impl PushSubscriber {
             return Ok(());
         };
 
-        let load_cache = true;
-        let response = http::get_client(context, load_cache)
-            .await?
-            .post("https://notifications.delta.chat/register")
-            .body(format!("{{\"token\":\"{token}\"}}"))
-            .send()
-            .await?;
-
-        let response_status = response.status();
-        if response_status.is_success() {
+        if http::post_string(
+            context,
+            "https://notifications.delta.chat/register",
+            format!("{{\"token\":\"{token}\"}}"),
+        )
+        .await?
+        {
             state.heartbeat_subscribed = true;
         }
         Ok(())