proxy: log endpoint name everywhere.

Checking out proxy logs for the endpoint is a frequent (often first) operation
during user issues investigation; let's remove endpoint id -> session id mapping
annoying extra step here.

proxy/src/auth/backend.rs

@@ -139,6 +139,16 @@ async fn auth_quirks(
 }
 
 impl BackendType<'_, ClientCredentials<'_>> {
+    /// Get compute endpoint name from the credentials.
+    pub fn get_endpoint(&self) -> Option<String> {
+        use BackendType::*;
+
+        match self {
+            Console(_, creds) => creds.project.clone(),
+            Postgres(_, creds) => creds.project.clone(),
+            Link(_) => Some("link".to_owned()),
+        }
+    }
     /// Authenticate the client via the requested backend, possibly using credentials.
     #[tracing::instrument(fields(allow_cleartext = allow_cleartext), skip_all)]
     pub async fn authenticate(

proxy/src/proxy.rs

@@ -455,6 +455,9 @@ impl<'a, S> Client<'a, S> {
 
 impl<S: AsyncRead + AsyncWrite + Unpin> Client<'_, S> {
     /// Let the client authenticate and connect to the designated compute node.
+    // Instrumentation logs endpoint name everywhere. Doesn't work for link
+    // auth; strictly speaking we don't know endpoint name in its case.
+    #[tracing::instrument(name = "", fields(ep = self.creds.get_endpoint().unwrap_or("".to_owned())), skip_all)]
     async fn connect_to_db(
         self,
         session: cancellation::Session<'_>,