Revert to raw Keycloak usernames in feature file

World parameter keys (StorageManagerUsername, DataConsumerUsername) resolve
to ctst_-prefixed usernames which lack the instanceIds Keycloak attribute
required by the management API. Use the base Keycloak usernames directly.

Issue: ZENKO-5202

Author: delthas

tests/ctst/features/reporting/StorageUsageReporting.feature

@@ -11,23 +11,23 @@ Feature: Storage Usage Reporting API
         Then the http response code is <expectedStatus>
 
         Examples:
-          | persona                  | expectedStatus |
-          | StorageManagerUsername   | 200            |
-          | DataConsumerUsername     | 403            |
+          | persona          | expectedStatus |
+          | storage_manager  | 200            |
+          | data_consumer    | 403            |
 
     @2.14.0
     @PreMerge
     @StorageUsageReporting
     Scenario: Storage usage report has a valid structure
-        Given an identity with the "StorageManagerUsername" keycloak persona
+        Given an identity with the "storage_manager" keycloak persona
         When the user retrieves the storage usage report
         Then the storage usage report response has a valid structure
 
     @2.14.0
     @PreMerge
     @StorageUsageReporting
     Scenario: Storage usage report contains multiple accounts
-        Given an identity with the "StorageManagerUsername" keycloak persona
+        Given an identity with the "storage_manager" keycloak persona
         And 2 additional accounts
         When the user retrieves the storage usage report
         Then the storage usage report contains the additional accounts
@@ -38,7 +38,7 @@ Feature: Storage Usage Reporting API
     @PrepareStorageUsageReportingScenarios
     Scenario Outline: Storage usage report returns accurate metrics
         Given the environment is set up with bucket created, test data uploaded, and count-items ran
-        And an identity with the "StorageManagerUsername" keycloak persona
+        And an identity with the "storage_manager" keycloak persona
         When the user retrieves the storage usage report
         Then the report contains the test account with location "<locationName>"
         And the report shows 3 objects and 600 bytes