[spark] Align spark.paimon.branch option with explicit branch syntax for chain tables

[juntaozhang]

Purpose

#8015

Tests

SparkChainTableITCase.testChainTableWithBranchOption

[leaves12138]

Thanks for the fix. I am holding off on approval for now because the current CI status still has a failing build_test job. Please fix or rerun it, then I can take another pass.

[juntaozhang]

Hi @leaves12138, appreciate your feedback, PTAL.
Thanks

[JingsongLi]

Reviewed with focus on alignment between the deprecated spark.paimon.branch option and the explicit Java/Paimon table$branch_xxx identifier path.

Applying the option before catalog.getTable(...) makes the Spark catalog resolve the same branched Identifier that explicit branch syntax would use, while leaving an explicit branch name untouched. I also verified the common Spark module compiles with:

mvn -pl paimon-spark/paimon-spark-common -am -Pfast-build -DskipTests compile

No additional blocker from my side.