feat: Add S3 access point support for cross-account table access

[JannicCutura]

Rationale for this change

Add support for accessing Iceberg tables via S3 access points, enabling cross-account access scenarios where organizations enforce access point usage instead of direct bucket access. Closes #2991.

I created this PR based on the contribution guide, but it is my first PR on an open source repo, so apologies in advance should I have missed any step.

Changes:

• Add S3_ACCESS_POINT_PREFIX config constant (s3.access-point.)
• Implement _resolve_s3_access_point() in PyArrowFileIO
• Implement _resolve_s3_access_point() in FsspecFileIO
• Add 12 unit tests (6 per FileIO implementation)

Configuration:

s3.access-point.<bucket-name> = <access-point-alias>

for example:

from pyiceberg.catalog import load_catalog
from pyiceberg.io import S3_ACCESS_POINT_PREFIX
    catalog = load_catalog(
        "glue",
        **{
            "type": "glue",
            "client.region": AWS_REGION,
            # Multiple buckets, each with its own access point
            "s3.access-point.bucket-a": "alias-a-123456-s3alias",
            f"{S3_ACCESS_POINT_PREFIX}bucket-b": "alias-b-789012-s3alias",

        }
    )

What

The access point alias (format: --s3alias) is used transparently in place of the bucket name when accessing S3 objects.

Why

Organizations increasingly enforce S3 access point usage for cross-account
data access instead of direct bucket access. This is common in enterprise
environments with strict security policies.

How

Introduces s3.access-point.<bucket> configuration that maps bucket names
to access point aliases. Both PyArrowFileIO and FsspecFileIO resolve these
at runtime, rewriting paths transparently.

Are these changes tested?

Yes.

• 12 unit tests added (6 for PyArrowFileIO, 6 for FsspecFileIO)
• Manually tested with real cross-account S3 access point on across two AWS accounts

Are there any user-facing changes?

No breaking changes. Existing configurations continue to work unchanged.
There is a new configuration option s3.access-point.<bucket-name>