Aliyun: Add Aliyun auth type for REST catalog

[yanggl29]

Backgroud

This PR adds built-in Alibaba Cloud authentication support for Iceberg REST
catalogs through rest.auth.type=aliyun.

It follows the dev-list discussion:

https://lists.apache.org/thread/2jrm755rzj3930wmgvcrtw73qzhnl44n

MaxCompute (ODPS) REST Catalog requests require Alibaba Cloud AK/SK signing.
Without built-in support, users must package and configure a custom
AuthManager JAR for each Spark, Flink, or other Iceberg deployment.

Changes

• Register aliyun as a built-in REST auth type.
• Add AliyunAuthManager and AliyunAuthSession.
• Add a pluggable AliyunRequestSigner interface.
• Add the ODPS signer with V2 and V4 signing support.
• Support AK/SK credentials, optional STS tokens, and environment-variable fallback.
• Add unit tests for manager loading, credential validation, request
  canonicalization, V2/V4 signing, STS tokens, paths, and headers.

The change is additive: existing defaults remain unchanged, no REST
specification files are modified, and no new external runtime dependency is
introduced.

Configuration

rest.auth.type=aliyun
aliyun.auth.signing-name=odps
aliyun.auth.access-key-id=<access-key-id>
aliyun.auth.access-key-secret=<access-key-secret>

# Optional: enable V4 signing
aliyun.auth.region=cn-hangzhou

# Optional: temporary credential
aliyun.auth.sts-token=<security-token>

Signing implementation

The ODPS canonical request and signing logic is adapted from the Alibaba Cloud
ODPS Java SDK release/0.58.x:

• AliyunRequestSigner.java
• SecurityUtils.java

Only the required signing logic is included to avoid depending on the full ODPS
SDK. The referenced sources are licensed under Apache License 2.0.

Feedback is especially welcome on the aliyun auth type name and the
provider-level signer abstraction.