imap: Add imap_client_vfuncs.send_tagline()

This allows plugins to catch all the IMAP command replies.

src/imap/imap-client.c

@@ -570,6 +570,12 @@ client_cmd_append_timing_stats(struct client_command_context *cmd,
 }
 
 void client_send_tagline(struct client_command_context *cmd, const char *data)
+{
+	cmd->client->v.send_tagline(cmd, data);
+}
+
+static void
+client_default_send_tagline(struct client_command_context *cmd, const char *data)
 {
 	struct client *client = cmd->client;
 	const char *tag = cmd->tag;
@@ -1415,5 +1421,6 @@ void clients_destroy_all(struct mail_storage_service_ctx *storage_service)
 struct imap_client_vfuncs imap_client_vfuncs = {
 	imap_state_export_base,
 	imap_state_import_base,
-	client_default_destroy
+	client_default_destroy,
+	client_default_send_tagline,
 };

src/imap/imap-client.h

@@ -130,6 +130,9 @@ struct imap_client_vfuncs {
 				const unsigned char *data, size_t size,
 				const char **error_r);
 	void (*destroy)(struct client *client, const char *reason);
+
+	void (*send_tagline)(struct client_command_context *cmd,
+			     const char *data);
 };
 
 struct client {