pool: add missing methods to the pooler interface

I added methods that are implemented but not included in the pooler interface.

Author: maxim-konovalov

CHANGELOG.md

@@ -13,6 +13,7 @@ Versioning](http://semver.org/spec/v2.0.0.html) except to the first release.
   connection and ctx is not canceled; 
   also added logs for error case of `ConnectionPool.tryConnect()` calls in 
   `ConnectionPool.controller()` and `ConnectionPool.reconnect()`
+- Methods that are implemented but not included in the pooler interface
 ### Changed
 
 ### Fixed

pool/pooler.go

@@ -1,15 +1,28 @@
 package pool
 
 import (
+	"context"
 	"time"
 
 	"github.com/tarantool/go-tarantool/v2"
 )
 
+// PoolerTopology is the interface that must be implemented by a connection pool and
+// describe topology methods.
+type PoolerTopology interface {
+	Add(ctx context.Context, instance Instance) error
+	Remove(name string) error
+}
+
 // Pooler is the interface that must be implemented by a connection pool.
 type Pooler interface {
+	PoolerTopology
+
 	ConnectedNow(mode Mode) (bool, error)
 	Close() []error
+	// CloseGraceful closes connections in the ConnectionPool gracefully. It waits
+	// for all requests to complete.
+	CloseGraceful() []error
 	ConfiguredTimeout(mode Mode) (time.Duration, error)
 	NewPrepared(expr string, mode Mode) (*tarantool.Prepared, error)
 	NewStream(mode Mode) (*tarantool.Stream, error)