proxy: update tokio-postgres to allow arbitrary config params (#8076)

## Problem

Fixes https://github.com/neondatabase/neon/issues/1287

## Summary of changes

tokio-postgres now supports arbitrary server params through the
`param(key, value)` method. Some keys are special so we explicitly
filter them out.

proxy/src/serverless/backend.rs

@@ -231,6 +231,10 @@ impl ConnectMechanism for TokioMechanism {
             .dbname(&self.conn_info.dbname)
             .connect_timeout(timeout);
 
+        config
+            .param("client_encoding", "UTF8")
+            .expect("client encoding UTF8 is always valid");
+
         let pause = ctx.latency_timer.pause(crate::metrics::Waiting::Compute);
         let res = config.connect(tokio_postgres::NoTls).await;
         drop(pause);

proxy/src/serverless/sql_over_http.rs

@@ -202,6 +202,7 @@ fn get_conn_info(
             options = Some(NeonOptions::parse_options_raw(&value));
         }
     }
+    ctx.set_db_options(params.freeze());
 
     let user_info = ComputeUserInfo {
         endpoint,