Clarify worker_pool host_label usage and fix blank entry in array

[bhpratt]

Four main changes:

• change worker pool host label to force new. It is not possible to update host labels on an existing worker pool after creation,
• fix length of array that creates a blank entry on read. example:

  ~ resource "ibm_satellite_cluster_worker_pool" "create_wp" {
      ~ host_labels        = [
          - "",
            # (2 unchanged elements hidden)
        ]
        id                 = "cdqf4juw0bl3s7phl9vg/cdqf4juw0bl3s7phl9vg-bddb143"
        name               = "test"

• update docs to clarify correct formatting of host labels
• update test due to errors w/duplicate ibm provider. since now using the default provider, switching regions to us-south

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Relates OR Closes #0000

Output from acceptance testing:

make testacc TEST=./ibm/service/satellite TESTARGS='-run=TestAccSatelliteClusterWorkerPool_Basic'
=== RUN   TestAccSatelliteClusterWorkerPool_Basic
--- PASS: TestAccSatelliteClusterWorkerPool_Basic (2176.31s)
PASS
ok      github.com/IBM-Cloud/terraform-provider-ibm/ibm/service/satellite       2177.473s

make testacc TEST=./ibm/service/satellite TESTARGS='-run=TestAccSatelliteCluster_Basic'

==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./ibm/service/satellite -v -run=TestAccSatelliteCluster_Basic -timeout 700m
=== RUN   TestAccSatelliteCluster_Basic
--- PASS: TestAccSatelliteCluster_Basic (4162.49s)
PASS
ok      github.com/IBM-Cloud/terraform-provider-ibm/ibm/service/satellite       4163.750s

[hkantare]

Even if user doesn't provide operating_system we always get "os" label ?

[bhpratt]

Correct. The service will automatically assign an OS label based on the operating system of the worker pool. Current options are RHEL7, RHEL8, and RHCOS.