Refactor: thread externalID and shared-VPC args through CreateHCPRoles explicitly

Summary

CreateHCPRoles in cmd/create/accountroles/creators.go currently reads args.externalID, args.route53RoleArn, and args.vpcEndpointRoleArn from package-global CLI state rather than accepting them as explicit parameters.

While this is not a live production risk (the function has no external callers today), it couples the function to the Cobra args global, making it harder to call from non-CLI contexts (e.g. tests, SDK consumers) and potentially causing stale-value bugs if the function is reused across calls in the future.

Desired behaviour

• Add externalID string as an explicit parameter to CreateHCPRoles.
• Thread externalID into buildRolesCreationInput via the parameter instead of args.externalID.
• Consider doing the same for route53RoleArn / vpcEndpointRoleArn (already passed as parameters, but still mutated into args inside the function on lines 328-329).
• Update all callers of CreateHCPRoles to pass the new parameter.

Context

Identified during review of PR #3264 (ROSAENG-57781 — opt-in STS external ID support).
Comment: https://github.com/openshift/rosa/pull/3264#discussion_r3389622445

Requested by: @olucasfreitas