feat: add reusable dsx-ci-go and dsx-ci-helm workflows

[huaweic-nv]

Summary

Two reusable workflows that DSX repos call with workflow_call:

Workflow	Purpose
dsx-ci-go.yml	Full Go CI: commitlint, license-headers, go-lint, go-test, docker-build, codeql, trufflehog, helm-validate, slack
dsx-ci-helm.yml	Helm CI: commitlint, license-headers, helm-validate, trufflehog, slack

Both accept an actions-ref input so callers pin all internal action refs to the same version — no @main drift.

Caller usage

# auth-callout ci.yml — entire CI in 12 lines
jobs:
  ci:
    uses: NVIDIA/dsx-github-actions/.github/workflows/dsx-ci-go.yml@v1
    with:
      go-version: "1.25.5"
      go-flags: "-mod=vendor"
      docker-image: dsx-exchange-auth-callout
      dockerfile: build/package/Dockerfile
      slack-channel-id: C09VC8R4E92
      actions-ref: v1
    secrets:
      SLACK_BOT_TOKEN: ${{ secrets.SLACK_BOT_TOKEN }}

Follow-up to #34 which added the composite actions these workflows use.

Jira: CDEVS-2228

Test plan

• dsx-ci-go.yml called from dsx-exchange-auth-callout
• dsx-ci-helm.yml called from dsx-exchange-deploy

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