Add support for Kubernetes 1.34

What does this MR do?

Add support for Kubernetes 1.34

• Add CI testing on GKE 1.34 and GKE 1.34 ARM.
• Move EKS testing from 1.32 to 1.33 (1.34 not available yet).
• Move vcluster testing from 1.33 to 1.34.
• Update user-facing and developer-facing docs.
• Drop legacy vcluster tests in favor of the new QA-compatible approach to DRY our pipelines.

Relates gitlab-org/distribution/team-tasks#1775 (closed)

Changelog: added

Related issues

Author checklist

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Required

For anything in this list which will not be completed, please provide a reason in the MR discussion.

• Merge Request Title and Description are up to date, accurate, and descriptive.
• MR targeting the appropriate branch.
• MR has a green pipeline.
• Documentation created/updated.
• Tests added/updated, and test plan for scenarios not covered by automated tests.
• Equivalent MR/issue for omnibus-gitlab opened.

Reviewers checklist

• MR has a green pipeline on https://gitlab.com/gitlab-org/charts/gitlab.
• Consider downstream impact to the Operator, as per evaluating impact from changes to GitLab chart.