feat(iaas): min/max acc tests (#811)

* feat(iaas): security group min/max acc test

* feat(iaas): image min/max acc test

* feat(iaas): KeyPair min/max acc test

* feat(iaas): Network area min/max acc test
- fix: wrong atLeast-validator for `minimum_prefix_length`

* feat(iaas): Network min/max acc test

* feat(iaas): Volume min/max acc test
- fix: volume update doesn't work if no name was defined
- fix: volume.server_id can not be set
- fix: error message volume.size returns value but was null

* feat(iaas): Network interfaces min/max acc test

* feat(iaas): Affinity groups acc test

* feat(iaas): Server min/max acc test
- stackit_server_volume_attach
- stackit_server_network_interface_attach
- stackit_server_service_account_attach

* fix(iaas): acc test
- image: fix read of Config.VirtioScsi
- keypair: add missing RequiresReplace() for name
- server: add missing UserData read in datasource and resource

* feat(iaas): public ip acc test
- fix: when a nic is assigned to a public ip, the field network_interface_id leads to recreation

stackit/internal/services/iaas/testdata/resource-network-interface-min.tf

@@ -0,0 +1,16 @@
+variable "project_id" {}
+variable "name" {}
+
+resource "stackit_network" "network" {
+  project_id = var.project_id
+  name       = var.name
+}
+
+resource "stackit_network_interface" "network_interface" {
+  project_id = var.project_id
+  network_id = stackit_network.network.network_id
+}
+
+resource "stackit_public_ip" "public_ip" {
+  project_id = var.project_id
+}