Set GPU Gres on all GPU nodes

[milliams]

Adds some Ansible magic to use a new variable nodegroups_map which contains instructions for matching node groups and injecting new data into them.

nodegroups_map:
  - key: "name"
    test: "match"
    args: ["gpu-.*"]
    inject:
      gres:
        - conf: "gpu:A100:1"
          file: "/dev/nvidia0"

says to find any node groups where the key ("name") matches "gpu-.*", and merge in the given inject dictionary.

So,

[
  {
    "name": "general-gen2-rack6"
  },
  {
    "name": "gpu-gpu1"
  }
]

becomes:

[
  {
    "name": "general-gen2-rack6"
  },
  {
    "name": "gpu-gpu1",
    "gres": {"conf": "gpu:A100:1", "file": "/dev/nvidia0"}
  }
]

This relates to isambard-sc/dl-bc5#17