Add initial support for bucket lifecycle (#7563)

This PR is based off @sinhaashish's PR for object lifecycle
management, which includes support only for,
- Expiration of object
- Filter using object prefix (_not_ object tags)

N B the code for actual expiration of objects will be included in a
subsequent PR.

pkg/lifecycle/noncurrentversion.go

@@ -0,0 +1,65 @@
+/*
+ * MinIO Cloud Storage, (C) 2019 MinIO, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package lifecycle
+
+import (
+	"encoding/xml"
+	"errors"
+)
+
+// NoncurrentVersionExpiration - an action for lifecycle configuration rule.
+type NoncurrentVersionExpiration struct {
+	XMLName        xml.Name `xml:"NoncurrentVersionExpiration"`
+	NoncurrentDays int      `xml:"NoncurrentDays,omitempty"`
+}
+
+// NoncurrentVersionTransition - an action for lifecycle configuration rule.
+type NoncurrentVersionTransition struct {
+	NoncurrentDays int    `xml:"NoncurrentDays"`
+	StorageClass   string `xml:"StorageClass"`
+}
+
+var (
+	errNoncurrentVersionExpirationUnsupported = errors.New("Specifying <NoncurrentVersionExpiration></NoncurrentVersionExpiration> is not supported")
+	errNoncurrentVersionTransitionUnsupported = errors.New("Specifying <NoncurrentVersionTransition></NoncurrentVersionTransition> is not supported")
+)
+
+// UnmarshalXML is extended to indicate lack of support for
+// NoncurrentVersionExpiration xml tag in object lifecycle
+// configuration
+func (n NoncurrentVersionExpiration) UnmarshalXML(d *xml.Decoder, startElement xml.StartElement) error {
+	return errNoncurrentVersionExpirationUnsupported
+}
+
+// UnmarshalXML is extended to indicate lack of support for
+// NoncurrentVersionTransition xml tag in object lifecycle
+// configuration
+func (n NoncurrentVersionTransition) UnmarshalXML(d *xml.Decoder, startElement xml.StartElement) error {
+	return errNoncurrentVersionTransitionUnsupported
+}
+
+// MarshalXML is extended to leave out
+// <NoncurrentVersionTransition></NoncurrentVersionTransition> tags
+func (n NoncurrentVersionTransition) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
+	return nil
+}
+
+// MarshalXML is extended to leave out
+// <NoncurrentVersionExpiration></NoncurrentVersionExpiration> tags
+func (n NoncurrentVersionExpiration) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
+	return nil
+}