include template_ids in library variable set datasource

[benPearce1]

Fixes: #652

For the terraform:

data "octopusdeploy_library_variable_sets" "platform" {
  partial_name = "Variable Set Name"
  space_id = data.octopusdeploy_space.space.id
  skip = 0
  take = 1
}

output "lvs_template_ids" {
    value = data.octopusdeploy_library_variable_sets.platform.library_variable_sets[0].template_ids
}

before:

Changes to Outputs:
  + lvs_template_ids = {}

after:

Changes to Outputs:
  + lvs_template_ids = {
      + "Common.TP.AnotherOne"    = "71a27af8-8372-4937-aa05-9ce7148df8b7"
      + "Common.TP.Environment"   = "28a603b4-6d4a-4356-b9b0-0ee530c09bdf"
      + "Common.TP.Something"     = "4415c144-9ab8-4306-a665-442e6429bd75"
      + "Common.TP.SomethingElse" = "805a1923-bcdb-4c30-80f6-b875c6f747fd"
      + "Common.TP.Target"        = "734a1e2b-2faa-4759-a652-b555c07eff88"
    }

[hnrkndrssn]

LGTM