Fix Base image build

[javanlacerda]

Title: Fix Cloud Build GPG errors and upgrade to Node.js 20 (LTS)

Summary
This PR resolves the build failures in the clusterfuzz-images project caused by missing or expired GPG keys in the legacy NodeSource installation scripts. It also upgrades the base environment to use Node.js 20 (LTS).

Problem
The existing docker/base build was failing with the following error:
GPG error: https://deb.nodesource.com/node_19.x focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 1655A0AB68576280

This was due to the use of the deprecated setup_19.x script and a Node.js version (19) that is no longer supported.

Solution

1. Upgraded to Node.js 20 (LTS): Migrated from Node 19 to the current stable Long Term Support version.
2. Modernized Installation Method: Replaced the legacy 15,000-line setup_19.x bash script with the modern, secure NodeSource installation method using /etc/apt/keyrings and a signed repository entry.
3. Binary Version Consistency: Updated the Ubuntu 24.04 Dockerfile to download and install the Node 20.12.2 (LTS) binary directly.
4. Cleanup: Removed the now-obsolete docker/base/setup_19.x script from the repository.

Changes

• docker/base/Dockerfile: Updated to use the new NodeSource apt repository method for Node 20.
• docker/base/ubuntu-20-04.Dockerfile: Updated to use the new NodeSource apt repository method for Node 20.
• docker/base/ubuntu-24-04.Dockerfile: Updated binary download URL and extraction logic for Node 20.12.2.
• docker/base/setup_19.x: Deleted.

Impact

• Fixes all base image builds in Cloud Build.
• Ensures the project uses a supported, secure version of Node.js.
• Reduces technical debt by removing legacy scripts in favor of standard Linux package management.