[fix](cloud) normalize SHOW PARTITIONS display for storage and replica (#60871)

[deardeng]

pick from #60871

In cloud mode, SHOW PARTITIONS now displays StorageMedium as OBJECT_STORAGE and ReplicaAllocation as . Also add PartitionsProcDirTest to cover cloud/non-cloud display behavior.

(cherry picked from commit 9688e57)

What problem does this PR solve?

Issue Number: close #xxx

Related PR: #xxx

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[yiguolei]

run buildall

[hello-stephen]

FE UT Coverage Report

Increment line coverage 15.38% (2/13) 🎉
Increment coverage report
Complete coverage report

[hello-stephen]

FE Regression Coverage Report

Increment line coverage 100.00% (13/13) 🎉
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