chore: Improve testkit package structure

[skhalash]

Description

Changes proposed in this pull request (what was done and why):

• Move all helpers to create different kinds of Kubernetes resources to the k8s package
• Consolidate package names no for telemetry generator mocks
• Lift apiserverproxy to the testkit root
• Rename otlp to otel since it the package functionality is not only limited to OTLP
• Bump Gingo CLI

Traceability

• The PR is linked to a GitHub issue.
• New features have a milestone set.
• New features have defined acceptance criteria in a corresponding GitHub Issue, and all criteria are satisfied with this PR.
• The corresponding GitHub issue has a respective area and kind label.
• The follow-up issues (if any) are linked in the Related Issues section.
• Adjusted the documentation if the change is user-facing.
• The feature is unit-tested
• The feature is e2e-tested

[kyma-bot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all