BE - Truncate service account first name to 90 characters

Summary

User accounts can have a first name up to 127 characters. However, if a flow name is longer (max 255) then a service account will fail to be created. We should truncate the user account limit to below 90 to stay consistent with decisions made in &20057.

We should make the change in the ItemConsumers::CreateService since this issue is related specifically to service accounts created for flows.

Context

gitlab-org/ai-powered/workflow-catalog/team-tasks#34 (comment 2912377997)

TBD

When working on this, please check with @amandarueda if we should actually take 127 characters (because this is technically possible) or rather 90 characters to stay consistent with decisions made in &20057.