feat(file_storage): support S3-compatible stores via endpoint_url and force_path_style
Adds two optional fields to the aws_s3 file storage config so the existing
backend can target S3-compatible object stores such as OCI Object Storage
or MinIO:
- endpoint_url: overrides the S3 endpoint. When unset, the endpoint is still
resolved from the region or AWS_ENDPOINT_URL_S3, as before.
- force_path_style: addresses buckets as <endpoint>/<bucket>. Required for
OCI, whose TLS certificate does not cover <bucket>.<namespace>.compat...
subdomains, so virtual-hosted requests fail with NotValidForName.
Both default to the current behaviour, so existing configs are unaffected.
Applies to [file_storage.aws_s3] and [theme.storage.aws_s3].