Add KV store providers (dynamic configuration only)

Co-authored-by: Jean-Baptiste Doumenjou <jb.doumenjou@gmail.com>

pkg/provider/kv/etcd/etcd.go

@@ -0,0 +1,25 @@
+package etcd
+
+import (
+	"github.com/abronan/valkeyrie/store"
+	"github.com/containous/traefik/v2/pkg/provider"
+	"github.com/containous/traefik/v2/pkg/provider/kv"
+)
+
+var _ provider.Provider = (*Provider)(nil)
+
+// Provider holds configurations of the provider.
+type Provider struct {
+	kv.Provider
+}
+
+// SetDefaults sets the default values.
+func (p *Provider) SetDefaults() {
+	p.Provider.SetDefaults()
+	p.Endpoints = []string{"127.0.0.1:2379"}
+}
+
+// Init the provider
+func (p *Provider) Init() error {
+	return p.Provider.Init(store.ETCDV3, "etcd")
+}