[develop] Fix DCV on Ubuntu 22.04+ by disabling Wayland

[hehe7318]

Description of changes

• Disable Wayland in GDM to ensure Xorg is used on headless GPU instances. Ubuntu 22.04+ defaults to Wayland which causes GDM startup issues with NVIDIA drivers and NICE DCV. Force Xorg by setting WaylandEnable=false in /etc/gdm3/custom.conf.

Tests

• Kitchen tests passed.
• The following integ tests also passed:

{%- import 'common.jinja2' as common with context -%}
{{- common.OSS_COMMERCIAL_X86.append("rocky8") or "" -}}
{{- common.OSS_COMMERCIAL_X86.append("rocky9") or "" -}}
---
test-suites:
  dcv:
    test_dcv.py::test_dcv_configuration:
      dimensions:
        # DCV on GPU enabled instance
        - regions: ["use1-az6"]
          instances: ["g4dn.2xlarge"]
          oss: ["rocky8"]
          schedulers: ["slurm"]
        # DCV on ARM + GPU
        - regions: ["use1-az6"]
          instances: ["g5g.2xlarge"]
          oss: ["rhel8"]
          schedulers: ["slurm"]
    test_dcv.py::test_dcv_with_remote_access:
      dimensions:
        - regions: ["ap-southeast-2"]
          instances: {{ common.INSTANCES_DEFAULT_X86 }}
          oss: [{{ DCV_OS_X86_1 }}]
          schedulers: ["slurm"]

Checklist

• Make sure you are pointing to the right branch.
• If you're creating a patch for a branch other than develop add the branch name as prefix in the PR title (e.g. [release-3.6]).
• Check all commits' messages are clear, describing what and why vs how.
• Make sure to have added unit tests or integration tests to cover the new/modified code.
• Check if documentation is impacted by this change.

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[himani2411]

Can you add a Unit Test for this as well as the check of which server Type we are using as part of Kitchen test?