segment_insert_function_instance doesn't work for Source Insert Function

[sp-aaflalo]

Description

Expect the provider to work also for source insert function, or have a ressource for it.

To Reproduce

Example Terraform code that triggers the issue:

resource "segment_function" "enrich_marketing_context" {
  code          = file("${path.module}/function/enrich-marketing-context.js")
  display_name  = "Enrich Marketing Context"
  resource_type = "INSERT_SOURCE"
  description   = "Function to add product=scalepad_marketing to context for Marketing source events"
  settings      = []
  logo_url      = "https://cdn.filepicker.io/api/file/RmPmpcBTQZKaFeGQrdG5"
}

resource "segment_insert_function_instance" "enrich_marketing_context" {
  for_each = local.custom_sources

  integration_id = segment_source.custom_sources[each.key].id
  function_id    = segment_function.enrich_marketing_context.id
  name           = "Enrich Context - ${each.key}"
  enabled        = true
  settings       = jsonencode({})
}