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.

pkg/madmin/config-help-commands.go

@@ -0,0 +1,49 @@
+/*
+ * 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 madmin
+
+import (
+	"io"
+	"net/http"
+	"net/url"
+)
+
+// HelpConfigKV - return help for a given sub-system.
+func (adm *AdminClient) HelpConfigKV(subSys, key string) (io.ReadCloser, error) {
+	v := url.Values{}
+	v.Set("subSys", subSys)
+	v.Set("key", key)
+	reqData := requestData{
+		relPath:     adminAPIPrefix + "/help-config-kv",
+		queryValues: v,
+	}
+
+	// Execute GET on /minio/admin/v2/help-config-kv
+	resp, err := adm.executeMethod(http.MethodGet, reqData)
+	if err != nil {
+		return nil, err
+	}
+
+	if resp.StatusCode != http.StatusOK {
+		defer closeResponse(resp)
+		return nil, httpRespToErrorResponse(resp)
+	}
+
+	return resp.Body, nil
+
+}