Support for CoreOS Satellite attach script:

[bhpratt]

Per requirements here: IBM-Cloud/terraform-provider-ibm#3838

Adding in support for the user to choose RHEL or RHCOS as the operating system for adding hosts to Satellite location

[bhpratt]

Tested locally. Used these setting

	controller := "<location-id>"
	labelMap := make(map[string]string)
	operatingSystem := "RHEL"
	attachSatHostOptions.Controller = &controller
	attachSatHostOptions.Labels = labelMap
	attachSatHostOptions.OperatingSystem = &operatingSystem

That correctly provided a RHEL script. No operatingSystem provided generated a RHEL attach script. RHCOS generated a CoreOS attach script. Other values for operatingSystem generated an error as expected.