Docker: upgrade HashiCorp tool versions

[ohmyfelix]

What changed

• Add GitHub Actions CI workflow to verify Docker image builds on every pull request to master
• Bump Nomad from 1.10.5 to 1.11.2
• Bump Consul from 1.21.5 to 1.22.3
• Bump Vault from 1.20.4 to 1.21.3
• Bump Terraform from 1.13.3 to 1.14.5
• Bump Packer from 1.14.2 to 1.15.0
• Keep Levant (0.4.0) and Waypoint (0.11.4) unchanged

Why

• Ensure Docker build validity is checked automatically during PR review
• Keep bundled HashiCorp CLIs current for security fixes, bug fixes, and compatibility improvements
• Reduce drift between this image and upstream stable releases