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/signature-v2.go

@@ -69,7 +69,7 @@ var resourceList = []string{
 }
 
 func doesPolicySignatureV2Match(formValues http.Header) APIErrorCode {
-	cred := globalServerConfig.GetCredential()
+	cred := globalActiveCred
 	accessKey := formValues.Get(xhttp.AmzAccessKeyID)
 	cred, _, s3Err := checkKeyValid(accessKey)
 	if s3Err != ErrNone {