No, ESU is not a general update that can be added in Gold Master image like what we do usually, it needs a complex process to apply.
Please refer to the following guide for a detailed process:
Obtaining Extended Security Updates for eligible Windows devices
https://techcommunity.microsoft.com/t5/windows-it-pro-blog/obtaining-extended-security-updates-for-eligible-windows-devices/ba-p/1167091
Other Reference:
FAQ about Windows 7 ESU
https://learn.microsoft.com/en-us/troubleshoot/windows-client/windows-7-eos-faq/windows-7-extended-security-updates-faq
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