Adds validation for slo_id#1221

TinaHeiligers merged 2 commits intoelastic:mainelastic/terraform-provider-elasticstack:mainfrom

TinaHeiligers:tpe1144/kbn_validate_slo_idTinaHeiligers/terraform-provider-elasticstack:tpe1144/kbn_validate_slo_idCopy head branch name to clipboard