[UI] read_basebackups ignores AWS_ENDPOINT for S3 list/get (MinIO/S3-compatible)

[eric-x-liu]

Problem

When AWS_ENDPOINT is set for S3-compatible storage (e.g. MinIO), the postgres-operator UI partially uses it in ui/operator_ui/spiloutils.py:

• read_stored_clusters and read_versions correctly use client('s3', endpoint_url=AWS_ENDPOINT).

In read_basebackups, the code still uses plain client('s3') for:

1. get_paginator('list_objects_v2') (listing backup sentinel files)
2. get_object when reading each *_backup_stop_sentinel.json

Those calls hit the default AWS endpoint, so the Backups tab can list cluster/version prefixes but fail or show empty data when loading base backup details against a custom endpoint.

This is the same class of issue as the older UI S3 endpoint discussion (e.g. #1028); the basebackup path was never aligned with the other helpers.

Suggested fix

Reuse a single s3_client = client('s3', endpoint_url=AWS_ENDPOINT) (or equivalent) for the paginator and get_object in read_basebackups, consistent with read_stored_clusters / read_versions.

Affected versions

Observed in v1.15.1; master still has the same client('s3') calls inside read_basebackups as of this report.

References

• https://github.com/zalando/postgres-operator/blob/master/ui/operator_ui/spiloutils.py (see read_basebackups)