Migrate config to KV data format (#8392)

- adding oauth support to MinIO browser (#8400) by @kanagaraj
- supports multi-line get/set/del for all config fields
- add support for comments, allow toggle
- add extensive validation of config before saving
- support MinIO browser to support proper claims, using STS tokens
- env support for all config parameters, legacy envs are also
  supported with all documentation now pointing to latest ENVs
- preserve accessKey/secretKey from FS mode setups
- add history support implements three APIs
  - ClearHistory
  - RestoreHistory
  - ListHistory
- add help command support for each config parameters
- all the bug fixes after migration to KV, and other bug
  fixes encountered during testing.

cmd/config/legacy.go

@@ -0,0 +1,55 @@
+/*
+ * 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 config
+
+import "github.com/minio/minio/pkg/auth"
+
+//// One time migration code section
+
+// SetCredentials - One time migration code needed, for migrating from older config to new for server credentials.
+func SetCredentials(c Config, cred auth.Credentials) {
+	c[CredentialsSubSys][Default] = KVS{
+		State:     StateOn,
+		Comment:   "Settings for credentials, after migrating config",
+		AccessKey: cred.AccessKey,
+		SecretKey: cred.SecretKey,
+	}
+}
+
+// SetRegion - One time migration code needed, for migrating from older config to new for server Region.
+func SetRegion(c Config, name string) {
+	c[RegionSubSys][Default] = KVS{
+		RegionName: name,
+		State:      StateOn,
+		Comment:    "Settings for Region, after migrating config",
+	}
+}
+
+// SetWorm - One time migration code needed, for migrating from older config to new for Worm mode.
+func SetWorm(c Config, b bool) {
+	// Set the new value.
+	c[WormSubSys][Default] = KVS{
+		State: func() string {
+			if b {
+				return StateOn
+			}
+			return StateOff
+		}(),
+		Comment: "Settings for WORM, after migrating config",
+	}
+}