storage: add http/https server and cert resover metrics (#11450)

## Problem
We need to export some metrics about certs/connections to configure
alerts and make sure that all HTTP requests are gone before turning
https-only mode on.
- Closes: https://github.com/neondatabase/cloud/issues/25526

## Summary of changes
- Add started connection and connection error metrics to http/https
Server.
- Add certificate expiration time and reload metrics to
ReloadingCertificateResolver.

safekeeper/src/http/mod.rs

@@ -31,6 +31,7 @@ pub async fn task_main_https(
     global_timelines: Arc<GlobalTimelines>,
 ) -> anyhow::Result<()> {
     let cert_resolver = ReloadingCertificateResolver::new(
+        "main",
         &conf.ssl_key_file,
         &conf.ssl_cert_file,
         conf.ssl_cert_reload_period,