fix(bucket): endpoint helper unconditionally forces https:// — original scheme lost for provisioned buckets #3317

Follow-up from review of #3270.

The endpoint helper unconditionally forces https:// for provisioned buckets. This is correct for the SeaweedFS/COSI ACME-ingress assumption that #3270 documents, but the producer strips the scheme into the Secret, so the original scheme is lost.

A hypothetical future COSI driver advertising a plain-http endpoint would be silently upgraded to https. Documented assumption, fine for the currently-supported config — worth revisiting if external-COSI support widens.

Non-blocking note raised during the LGTM review of #3270.