[luxembourg][mi300x] Add mi300x cluster (WIP)

input/grid5000/sites/luxembourg/clusters/mi300x/mi300x.yaml

+---
+model: Dell PowerEdge XE9680
+created_at: 2025-01-06
+kavlan: true
+boot_type: uefi
+exotic: false # TODO: specify if 'true' or 'false'
+queues:
+  - admin
+  - testing
+nodes:
+  mi300x-1:
+    chassis:
+      manufactured_at: 1970-01-01 # TODO: Put date.
+      warranty_end: 2028-06-15
+    supported_job_types:
+      deploy: true
+      besteffort: true
+      max_walltime: 0
+    processor:
+      microarchitecture: Haswell # TODO: replace with microarch name.
+      clock_speed: 8 # TODO: Replace with clock speed.
+    network_adapters:
+      bmc:
+        enabled: true
+        mountable: false
+        mounted: false
+      eth0:
+        enabled: true
+        mountable: true
+        mounted: true
+    storage_devices:
+      disk0: # This field will have to be renamed later.
+        id: disk0
+        interface: SAS
+        by_path: "/dev/disk/by-path/dummy" # this path will have to change later.
+    software:
+      standard-environment: debian11-x64-std
+    management_tools:
+      bmc_vendor_tool: racadm
+    nodeset: mi300x