The "tier" variable should not be required on web apps modules

[lucacavallaro]

Issue

tier is required, but is only needed when app_service_plan_id is null

Affected modules

• azure_app_service
• azure_function_app

Current variable definition

variable "tier" {
  type        = string
  description = "Resource tiers depending on demanding workload. Allowed values are 'premium', 'standard', 'test'. Note, \"test\" does not support deployment slots."
  default     = "premium"

  validation {
    condition     = contains(["premium", "standard", "test"], var.tier)
    error_message = "Allowed values for \"tier\" are \"premium\", \"standard\", or \"test\". Note, \"test\" does not support deployment slots."
  }
}