etcd: Add world API changes for watching member status

This adds some useful functionality so that anyone with access to the
world API, can learn information about the changing etcd cluster it's
using.

etcd/interfaces/const.go

@@ -0,0 +1,30 @@
+// Mgmt
+// Copyright (C) 2013-2023+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package interfaces
+
+import (
+	"time"
+)
+
+const (
+	// MemberChangePollingInterval is the polling interval to use when
+	// watching for member changes for client operations. This is basically
+	// the same idea in the core package named MemberChangeInterval, but
+	// held separately for now.
+	MemberChangePollingInterval = 1000 * time.Millisecond
+)