Update javadoc for updateTestPlanAttributes method

- Document the complete replacement behavior of the method
- Explain the clearing of existing attributes collection to prevent Hibernate conflicts
- Clarify handling of empty/null attributes parameter

Author: imashkanov

src/main/java/com/epam/ta/reportportal/core/tms/service/TmsTestPlanAttributeService.java

@@ -8,6 +8,18 @@ public interface TmsTestPlanAttributeService {
 
   void createTestPlanAttributes(TmsTestPlan tmsTestPlan, List<TmsTestPlanAttributeRQ> attributes);
 
+  /**
+   * Updates test plan attributes by completely replacing existing attributes with new ones.
+   * This method first deletes all existing attributes and then creates new ones.
+   * 
+   * Note: This method clears the existing attributes collection from the test plan entity
+   * to prevent Hibernate session conflicts when attributes with the same attributeId 
+   * are being replaced.
+   *
+   * @param existingTestPlan The test plan to update attributes for.
+   * @param attributes       The new list of attributes to set. If empty or null, 
+   *                        all existing attributes will be removed.
+   */
   void updateTestPlanAttributes(TmsTestPlan existingTestPlan,
       List<TmsTestPlanAttributeRQ> attributes);