Expose flatcar-install OEM parameter

By exposing this parameter it is possible to install OEM specific software
during the `flatcar-install` invocation.

bare-metal/flatcar-linux/kubernetes/worker/butane/install.yaml

@@ -35,6 +35,7 @@ storage:
             -d ${install_disk} \
             -C ${os_channel} \
             -V ${os_version} \
+            -o ${oem_type} \
             ${baseurl_flag} \
             -i ignition.json
           udevadm settle

bare-metal/flatcar-linux/kubernetes/worker/matchbox.tf

@@ -50,6 +50,7 @@ data "ct_config" "install" {
     mac                = var.mac
     install_disk       = var.install_disk
     ssh_authorized_key = var.ssh_authorized_key
+    oem_type           = var.oem_type
     # only cached profile adds -b baseurl
     baseurl_flag = var.cached_install ? "-b ${var.matchbox_http_endpoint}/assets/flatcar" : ""
   })

bare-metal/flatcar-linux/kubernetes/worker/variables.tf

@@ -98,6 +98,12 @@ variable "kernel_args" {
   default     = []
 }
 
+variable "oem_type" {
+  type        = string
+  default     = ""
+  description = "An OEM type to install with flatcar-install."
+}
+
 # unofficial, undocumented, unsupported
 
 variable "service_cidr" {