Update image-builder.md - Add a sleep delay to the customizations script

[mbiver]

This executes too rapidly and many times the image isn't ready for the quickstart json to run inside the VM. You end up with a (PackerBuildFailed) and if you look in the customization.log, you'll see messages like the below. If the OS just has a little bit of time to fully come up, though, before the customizations, the error goes away.

[7111a125-9cce-4cc6-80f1-70030c08e815] PACKER 2025/03/18 20:42:48 ui: azure-arm: E: Could not open file /var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_focal-updates_main_i18n_Translation-en - open (2: No such file or directory)
[7111a125-9cce-4cc6-80f1-70030c08e815] PACKER 2025/03/18 20:42:48 ui: azure-arm: E: Could not open file /var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_focal-updates_main_binary-amd64_Packages - open (2: No such file or directory)
[7111a125-9cce-4cc6-80f1-70030c08e815] PACKER 2025/03/18 20:42:48 ui: azure-arm: E: Could not open file /var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_focal_restricted_i18n_Translation-en - open (2: No such file or directory)
[7111a125-9cce-4cc6-80f1-70030c08e815] PACKER 2025/03/18 20:42:48 ui: azure-arm: E: Could not open file /var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_focal_restricted_binary-amd64_Packages - open (2: No such file or directory)
[7111a125-9cce-4cc6-80f1-70030c08e815] PACKER 2025/03/18 20:42:48 ui: azure-arm: E: Could not open file /var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_focal_main_i18n_Translation-en - open (2: No such file or directory)
[7111a125-9cce-4cc6-80f1-70030c08e815] PACKER 2025/03/18 20:42:48 ui: azure-arm: E: Could not open file /var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_focal_main_binary-amd64_Packages - open (2: No such file or directory)
[7111a125-9cce-4cc6-80f1-70030c08e815] PACKER 2025/03/18 20:42:48 [INFO] 2138 bytes written for 'stdout'
[7111a125-9cce-4cc6-80f1-70030c08e815] PACKER 2025/03/18 20:42:48 packer-plugin-azure_v2.2.0_x5.0_linux_amd64 plugin: 2025/03/18 20:42:48 [ERROR] Remote command exited with '100': chmod +x /tmp/script_3400.sh; sudo '/tmp/script_3400.sh'
[7111a125-9cce-4cc6-80f1-70030c08e815] PACKER 2025/03/18 20:42:48 packer-plugin-azure_v2.2.0_x5.0_linux_amd64 plugin: 2025/03/18 20:42:48 [INFO] RPC endpoint: Communicator ended with: 100
[7111a125-9cce-4cc6-80f1-70030c08e815] PACKER 2025/03/18 20:42:48 [INFO] 0 bytes written for 'stderr'

[prmerger-automator]

@mbiver : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change.

[learn-build-service-prod]

Learn Build status updates of commit 39f7233:

✅ Validation status: passed

File	Status	Preview URL	Details
articles/virtual-machines/linux/image-builder.md	✅Succeeded

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[v-dirichards]

@kof-f

Can you review the proposed changes?

Important: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

#label:"aq-pr-triaged"
@MicrosoftDocs/public-repo-pr-review-team