[DEVOPS-3893] ci: add docker scout action

[Dion Gionet Mallet (dion-gionet)]

Description

This PR adds Docker Scout vulnerability scanning to the Docker image build workflows.

Changes Made

• Added Docker Scout action step to build-image.yml
• Configured to scan for critical and high severity vulnerabilities
• Set to ignore base image vulnerabilities and provide summary output

Docker Scout Configuration

- name: Docker Scout
  uses: docker/scout-action@v1
  with:
    command: cves
    image: devolutions/prux:${{ inputs.tag }}
    ignore-base: true
    only-severities: critical,high
    summary: true

Testing

• Workflow runs successfully with Docker Scout
• Vulnerability scan results are displayed in job output
• No breaking changes to existing build process

Related Issues

• DEVOPS-3893: Add Docker Scout to all Docker build workflows

Additional Notes

This is part of a larger initiative to add Docker Scout vulnerability scanning to all Docker image build workflows across the Devolutions organization for improved security posture.