feat: set appname for pg_stat_activity entry

This is so `select * from pg_stat_activity where application_name like '%pg_net%';`
can work as usual.

src/worker.c

@@ -102,6 +102,7 @@ void pg_net_worker(Datum main_arg) {
   BackgroundWorkerUnblockSignals();
 
   BackgroundWorkerInitializeConnection(guc_database_name, guc_username, 0);
+  pgstat_report_appname("pg_net " EXTVERSION); // set appname for pg_stat_activity
 
   elog(INFO, "pg_net_worker started with a config of: pg_net.ttl=%s, pg_net.batch_size=%d, pg_net.username=%s, pg_net.database_name=%s", guc_ttl, guc_batch_size, guc_username, guc_database_name);
 

test/test_user_db.py

@@ -32,3 +32,17 @@ def test_net_with_different_username_dbname(sess):
 
     # bg worker restarts after 1 second
     time.sleep(1.1)
+
+
+def test_net_appname(sess):
+    """Check that pg_stat_activity has appname set"""
+
+    ## can use the net.worker_restart function
+    (count,) = sess.execute(
+        text(
+            """
+        select count(1) from pg_stat_activity where application_name like '%pg_net%';
+    """
+        )
+    ).fetchone()
+    assert count == 1