[Fix] Support show proc '/colocation_group/{group_id}' in cloud mode

[C1R2S3]

Fixes #55756

Problem:
In Cloud Mode, executing SHOW PROC '/colocation_group/{group_id}' returns empty results, while it works in Local Mode.

Solution:
Added a new method lookupForCloud in ColocationGroupProcDir.
This method retrieves the backend distribution from CloudSystemInfoService,
ensuring consistent behavior with Local Mode.

[Thearas]

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1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
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[deardeng]

https://github.com/apache/doris/pull/59685/files 这里看起来有个一样fix的pr

建议这个pr，也加个测试case