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/event/target/elasticsearch.go

@@ -31,6 +31,22 @@ import (
 	"gopkg.in/olivere/elastic.v5"
 )
 
+// Elastic constants
+const (
+	ElasticFormat     = "format"
+	ElasticURL        = "url"
+	ElasticIndex      = "index"
+	ElasticQueueDir   = "queue_dir"
+	ElasticQueueLimit = "queue_limit"
+
+	EnvElasticState      = "MINIO_NOTIFY_ELASTICSEARCH_STATE"
+	EnvElasticFormat     = "MINIO_NOTIFY_ELASTICSEARCH_FORMAT"
+	EnvElasticURL        = "MINIO_NOTIFY_ELASTICSEARCH_URL"
+	EnvElasticIndex      = "MINIO_NOTIFY_ELASTICSEARCH_INDEX"
+	EnvElasticQueueDir   = "MINIO_NOTIFY_ELASTICSEARCH_QUEUE_DIR"
+	EnvElasticQueueLimit = "MINIO_NOTIFY_ELASTICSEARCH_QUEUE_LIMIT"
+)
+
 // ElasticsearchArgs - Elasticsearch target arguments.
 type ElasticsearchArgs struct {
 	Enable     bool     `json:"enable"`