fix(dcv): Optimize Ubuntu DCV installation and prevent restart prompts

- Add NEEDRESTART_MODE=l environment variable to suppress needrestart prompts during installation
- Install ubuntu-desktop with --no-install-recommends flag to reduce unnecessary package dependencies
- Update unit tests to verify NEEDRESTART_MODE is set and ubuntu-desktop installation uses --no-install-recommends
- Prevents interactive restart dialogs during automated DCV setup on Ubuntu systems

Author: gmarciani

cookbooks/aws-parallelcluster-platform/resources/dcv/partial/_ubuntu_common.rb

@@ -45,8 +45,9 @@ def pre_install
       code <<-PREREQ
         set -e
         DEBIAN_FRONTEND=noninteractive
+        NEEDRESTART_MODE=l
         apt -y install whoopsie
-        apt -y install ubuntu-desktop && apt -y install mesa-utils || (dpkg --configure -a && exit 1)
+        apt -y install --no-install-recommends ubuntu-desktop && apt -y install mesa-utils || (dpkg --configure -a && exit 1)
         apt -y purge ifupdown
         wget https://d1uj6qtbmh3dt5.cloudfront.net/NICE-GPG-KEY
         gpg --import NICE-GPG-KEY

cookbooks/aws-parallelcluster-platform/spec/unit/resources/dcv_spec.rb

@@ -472,8 +472,9 @@ def self.nothing(chef_run)
           when 'ubuntu'
             is_expected.to periodic_apt_update('')
             is_expected.to run_bash('install pre-req').with_cwd(Chef::Config[:file_cache_path]).with_retries(10).with_retry_delay(5)
+                                                      .with_code(/NEEDRESTART_MODE=l/)
                                                       .with_code(/apt -y install whoopsie/)
-                                                      .with_code(/apt -y install ubuntu-desktop && apt -y install mesa-utils || (dpkg --configure -a && exit 1)/)
+                                                      .with_code(/apt -y install --no-install-recommends ubuntu-desktop && apt -y install mesa-utils || \(dpkg --configure -a && exit 1\)/)
                                                       .with_code(/apt -y purge ifupdown/)
                                                       .with_code(%r{wget https://d1uj6qtbmh3dt5.cloudfront.net/NICE-GPG-KEY})
           when 'amazon'