Add endpoints for managing IAM policies (#15897)

Co-authored-by: Taran <taran@minio.io>
Co-authored-by: ¨taran-p¨ <¨taran@minio.io¨>
Co-authored-by: Aditya Manthramurthy <donatello@users.noreply.github.com>

cmd/api-errors.go

@@ -195,6 +195,8 @@ const (
 	ErrBucketTaggingNotFound
 	ErrObjectLockInvalidHeaders
 	ErrInvalidTagDirective
+	ErrPolicyAlreadyAttached
+	ErrPolicyNotAttached
 	// Add new error codes here.
 
 	// SSE-S3/SSE-KMS related API errors
@@ -1939,6 +1941,16 @@ var errorCodes = errorCodeMap{
 		Description:    "Invalid checksum provided.",
 		HTTPStatusCode: http.StatusBadRequest,
 	},
+	ErrPolicyAlreadyAttached: {
+		Code:           "XMinioPolicyAlreadyAttached",
+		Description:    "The specified policy is already attached.",
+		HTTPStatusCode: http.StatusConflict,
+	},
+	ErrPolicyNotAttached: {
+		Code:           "XMinioPolicyNotAttached",
+		Description:    "The specified policy is not found.",
+		HTTPStatusCode: http.StatusNotFound,
+	},
 	// Add your error structure here.
 }