chore(core): bump golang base image in dlv Dockerfiles

[LopatinDmitr]

Description

Update the Golang builder image version in the delve-related Dockerfiles.

Why do we need it, and what problem does it solve?

The debug image Dockerfiles still used an older Golang base image. Bumping them to 1.25.8 keeps these builder images aligned with the current toolchain and includes the latest upstream base image updates.

What is the expected result?

1. Build dlv-apiserver, dlv-audit, and dlv-controller Dockerfiles.
2. Verify they use golang:1.25.8-bookworm as the builder image.
3. Ensure the debug image build stages complete successfully.

Checklist

• The code is covered by unit tests.
• e2e tests passed.
• Documentation updated according to the changes.
• Changes were tested in the Kubernetes cluster manually.

Changelog entries

section: core
type: chore
summary: Bump Golang base image to 1.25.8 in delve Dockerfiles.
impact_level: low