Update on-disk storage format for users system (#7949)

- Policy mapping is now at `config/iam/policydb/users/myuser1.json`
  and includes version.

- User identity file is now versioned.

- Migrate old data to the new format.

cmd/admin-handlers.go

@@ -1253,7 +1253,7 @@ func (a adminAPIHandlers) SetUserPolicy(w http.ResponseWriter, r *http.Request)
 		return
 	}
 
-	if err := globalIAMSys.SetUserPolicy(accessKey, policyName); err != nil {
+	if err := globalIAMSys.PolicyDBSet(accessKey, policyName); err != nil {
 		writeErrorResponseJSON(ctx, w, toAdminAPIErr(ctx, err), r.URL)
 	}
 

cmd/sts-handlers.go

@@ -183,7 +183,7 @@ func (sts *stsAPIHandlers) AssumeRole(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	policyName, err := globalIAMSys.GetUserPolicy(user.AccessKey)
+	policyName, err := globalIAMSys.PolicyDBGet(user.AccessKey)
 	if err != nil {
 		logger.LogIf(ctx, err)
 		writeSTSErrorResponse(w, stsErrCodes.ToSTSErr(ErrSTSInvalidParameterValue))