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/policy/opa/help.go

@@ -0,0 +1,29 @@
+/*
+ * 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 opa
+
+import "github.com/minio/minio/cmd/config"
+
+// Help template for OPA policy feature.
+var (
+	Help = config.HelpKV{
+		URL:            `Points to URL for OPA HTTP API endpoint. eg: "http://localhost:8181/v1/data/httpapi/authz/allow"`,
+		AuthToken:      "Authorization token for the OPA HTTP API endpoint (optional)",
+		config.State:   "Indicates if OPA policy is enabled or not",
+		config.Comment: "A comment to describe the OPA policy setting",
+	}
+)