Add Node 24 | Remove Node 18 EOL | Tweak CI

[dbpolito]

This pull request updates the project to include support for Node.js 24 while deprecating Node.js 18. It also introduces a new 22-nginx variant and updates the CI/CD workflows, build scripts, and documentation accordingly.

Node.js Version Updates:

• Updated the base image in 24/Dockerfile from node:18-alpine to node:24-alpine, renaming the file from 18/Dockerfile to 24/Dockerfile.
• Updated the fwd-template.json file to replace the Node.js 18 configuration with Node.js 24, and shifted other versions accordingly (e.g., Node.js 20 replaces 18, and Node.js 22 replaces 20). [1] [2] [3]

CI/CD Workflow Updates:

• Updated the runs-on parameter in .github/workflows/ci-cd.yml to use ubuntu-24.04 and ubuntu-24.04-arm instead of ubuntu-latest and buildjet-4vcpu-ubuntu-2204-arm. [1] [2]

Build Script Enhancements:

• Updated kool.yml to remove the Node.js 18 build step and add build steps for Node.js 24 and the new 22-nginx variant.

Documentation Updates:

• Removed references to Node.js 18 from the README.md and added entries for Node.js 24 and the 22-nginx variant under "Available Tags." [1] [2]
• Moved Node.js 18 to the "Legacy tags" section in the README.md.