Use ci user to pull images & update GDK image digest

What does this MR do and why?

The MR has 2 updates:

1. Update GDK image digest to keep up to date
2. Use default CI user instead of Analytics specific user for pulling docker images.
   • This simplifies configuration and does not require ANALYTICS_REGISTRY_PASS, ANALYTICS_REGISTRY_HOST, ANALYTICS_REGISTRY_USER env variables for the e2e tests any longer.
   • It is also needed to fix an issue where gitlab-qa-ee image can not be pulled from gitlab-org/security/gitlab mirror - https://gitlab.com/gitlab-org/security/gitlab/-/issues/1182.

Screenshots or screen recordings

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How to set up and validate locally

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MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.