Add tests for different Postgres client libraries (#2008)

* Add tests for different postgres clients
* test/fixtures: sanitize test name for test_output_dir
* test/fixtures: do not look for etcd before runtime
* Add workflow for testing Postgres client libraries

test_runner/pg_clients/csharp/npgsql/Program.cs

@@ -0,0 +1,19 @@
+using Npgsql;
+
+var host = Environment.GetEnvironmentVariable("NEON_HOST");
+var database = Environment.GetEnvironmentVariable("NEON_DATABASE");
+var user = Environment.GetEnvironmentVariable("NEON_USER");
+var password = Environment.GetEnvironmentVariable("NEON_PASSWORD");
+
+var connString = $"Host={host};Username={user};Password={password};Database={database}";
+
+await using var conn = new NpgsqlConnection(connString);
+await conn.OpenAsync();
+
+await using (var cmd = new NpgsqlCommand("SELECT 1", conn))
+await using (var reader = await cmd.ExecuteReaderAsync())
+{
+    while (await reader.ReadAsync())
+        Console.WriteLine(reader.GetInt32(0));
+}
+await conn.CloseAsync();