doc: Mention import operation on use auto-scaling per shard documentation

[oarbusi]

Description

Mention import operation on use auto-scaling per shard documentation

Link to any related issue(s): CLOUDP-308513

Type of change:

• Bug fix (non-breaking change which fixes an issue). Please, add the "bug" label to the PR.
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• This change requires a documentation update
• Documentation fix/enhancement

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Further comments

[github-actions]

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[AgustinBettati]

This statement can be misinterpreted, a imported cluster that was already using latest ISS config can have shard mode. Maybe we can unify with the note above and mention something like:

There can be specific scenarios in which you reach an advanced_cluster configuration using new sharding configuration but does not have shard-level auto-scaling:

• Configuration using single replication_specs per shard was defined prior to version 1.23.0 in which auto-scaling per shard feature was released.
• Cluster defined with legacy schema (e.g. mongodbatlas_cluster or mongodbatlas_advanced_cluster using num_shards > 1) is imported into mongodbatlas_advanced_cluster using single replication_specs per shard.

For these scenarios an update to the cluster configuration must be made to activate the auto-scaling per shard feature. An example for achieving this can be temprorily modifying the value of compute_min_instance.

[oarbusi]

Thanks for the suggestion. What do you think of the changes in 8c028f8?

[corryroot]

LGTM! I commented with some small copy fixes.

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[AgustinBettati]

Thank you for the follow ups 👌