[Bug] OBS filesystem loader should not require access and secret key

[thswlsqls]

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Paimon version
master @ 526b91f (2.1-SNAPSHOT)

Compute Engine
Engine-agnostic (core FileIO); surfaces in any Flink/Spark/Hive catalog on obs://.

Minimal reproduce step

1. Create a catalog with warehouse = 'obs://<bucket>/warehouse', fs.obs.endpoint and fs.obs.security.provider, without static access/secret keys.
2. Any table operation fails with UnsupportedSchemeException: Could not find a file io implementation for scheme 'obs' in the classpath.

OBSLoader.requiredOptions() declares fs.obs.access.key and fs.obs.secret.key. Required options are a selection gate (FileIOLoader.requiredOptions() Javadoc): when one is absent, FileIO.get() discards the loader and falls back to HadoopFileIO, which cannot resolve OBSFileSystem — it lives in the plugin-only classloader.

What doesn't meet your expectations?
hadoop-huaweicloud authenticates without static keys, through fs.obs.security.provider (IObsCredentialsProvider, e.g. ECS agency) or a Hadoop credential provider. Those configurations should route through the bundled OBS plugin instead of being gated out. fs.obs.endpoint should stay required: DefaultOBSClientFactory reads it without a default.

Anything else?
The same defect was reported and fixed for S3 in #8674 / #8679.

Are you willing to submit a PR?

• I'm willing to submit a PR!