chore: Refactor getClusterSharding and add proper unit-tests

[leoluz]

The getClusterSharding function is currently implemented in the commands package. This function has important logic that must be properly unit-tested. The commands packages should be kept as lean as possible without any business logic as there are no tests currently in the majority of those packages.

Suggestion:

• refactor the getClusterSharding function moving it out of the commands package. The package /controller/sharding seems to be a better place to expose this functionality.
• The function getClusterSharding needs to have extensive unit test coverage as it drives important logic on how to infer shardings based on different configurations.

Related to #17016 and #17124

Checklist:

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