feat: Ensures asymmetric auto-scaling is not defined in the cluster when using the old sharding configuration in mongodbatlas_advanced_cluster

[oarbusi]

Description

Uses old SDK version when the old schema structure is used for mongodbatlas_advanced_cluster

This has been also tested manually creating these 2 clusters:

resource "mongodbatlas_advanced_cluster" "test-node-2" {
  project_id   = var.project_id
  name         = "OLD-SCHEMA-CLUSTER"
  cluster_type = "SHARDED"

  replication_specs {
    num_shards = 2 
    region_configs {
      electable_specs {
        instance_size = "M30"
        disk_iops = 3000
        node_count    = 3
      }
      provider_name = "AWS"
      priority      = 7
      region_name   = "EU_WEST_1"
    }
  }
}

resource "mongodbatlas_advanced_cluster" "test-no-node" {
  project_id   = var.project_id
  name         = "NEW-SCHEMA-CLUSTER"
  cluster_type = "SHARDED"

  replication_specs { # first shard
    region_configs {
      electable_specs {
        instance_size = "M10"
        disk_iops = 3000
        node_count    = 3
      }
      provider_name = "AWS"
      priority      = 7
      region_name   = "EU_WEST_1"
    }
  }

  replication_specs { # second shard
    region_configs {
      electable_specs {
        instance_size = "M10"
        disk_iops = 3000
        node_count    = 3
      }
      provider_name = "AWS"
      priority      = 7
      region_name   = "EU_WEST_1"
    }
  }
}

and then checking for the auto-scaling mode of each cluster.
For the cluster named OLD-SCHEMA-CLUSTER it is "autoScalingMode" : "CLUSTER",
For the cluster named NEW-SCHEMA-CLUSTER it is "autoScalingMode" : "SHARD",

Link to any related issue(s): CLOUDP-285705

Type of change:

• Bug fix (non-breaking change which fixes an issue). Please, add the "bug" label to the PR.
• New feature (non-breaking change which adds functionality). Please, add the "enhancement" label to the PR. A migration guide must be created or updated if the new feature will go in a major version.
• Breaking change (fix or feature that would cause existing functionality to not work as expected). Please, add the "breaking change" label to the PR. A migration guide must be created or updated.
• This change requires a documentation update
• Documentation fix/enhancement

Required Checklist:

• I have signed the MongoDB CLA
• I have read the contributing guides
• I have checked that this change does not generate any credentials and that they are NOT accidentally logged anywhere.
• I have added tests that prove my fix is effective or that my feature works per HashiCorp requirements
• I have added any necessary documentation (if appropriate)
• I have run make fmt and formatted my code
• If changes include deprecations or removals I have added appropriate changelog entries.
• If changes include removal or addition of 3rd party GitHub actions, I updated our internal document. Reach out to the APIx Integration slack channel to get access to the internal document.

Further comments

[lantoli]

@oarbusi cc @EspenAlbert as this is a change to adv_cluster that is not done also in tpf, can you please update the readme file so we don't miss to do this in tpf? https://github.com/mongodb/terraform-provider-mongodbatlas/tree/master/internal/service/advancedclustertpf#changes-in-advancedcluster-that-needs-to-be-added-here
thanks

[oarbusi]

@lantoli done in bd76cda

[AgustinBettati]

LGTM! Some minor suggestions

[cveticm]

lgtm!

[corryroot]

LGTM!

[oarbusi]

Test failure is not related to this PR. Merging anyway