[cosn] Support alternative COSN authentication options

[thswlsqls]

Purpose

fix #10129

• Accept fs.cosn.bucket.endpoint_suffix instead of region during plugin selection and leave credentials to the hadoop-cos provider chain.
• Preserve region-based selection and mirror the OBS fix in [filesystem][obs] Remove access key and secret from required options in OBSLoader #8958.

Tests

• COSNLoaderTest: endpoint suffix with default/custom provider configuration and region without static credentials; 3/3 passed.
• Restoring only COSNLoader.java from upstream/master produced 3/3 errors; fixed HEAD passed 3/3.
• mvn -pl paimon-filesystems/paimon-cosn -DfailIfNoTests=false clean install passed on JDK 11, including checkstyle, spotless, enforcer, and surefire.

[JingsongLi]

This addresses a real configuration failure: FileIO.get(cosn://...) previously rejected endpoint-suffix and provider-chain setups before the bundled hadoop-cos implementation could authenticate. The loader change is appropriately narrow, preserves region selection, and COSNFileIO.configure forwards fs.cosn.* options to Hadoop.

I applied the PR patch and ran COSNLoaderTest on both JDK 8 and JDK 11: 3/3 passed in each run. These tests verify plugin selection; they do not exercise actual environment/custom credential acquisition or an object-store operation. Please provide an integration or documented staging validation for the intended provider chain before production rollout. The current PR checks also include a failing JDK 11 Core and integrations lane (plus the aggregate result); establish the cause or get CI green before merge. The change has end-to-end value and I found no confirmed code defect in the loader.