Enhance tagging strategy and GitHub Actions workflow

[alchatti]

This pull request significantly enhances the Docker image build and publish workflow by introducing support for multiple OS variants, improving tag management, and making the workflow more flexible and maintainable. The changes include expanding the build matrix, generating detailed and consistent Docker tags, and streamlining metadata handling for images.

Build matrix and tag improvements:

• Expanded the build matrix to include both multiple PHP versions (php) and multiple OS versions (os), enabling builds for all combinations of PHP 8.1, 8.2, 8.3 and OSes "bookworm" and "trixie".
• Updated Docker build arguments to use the new matrix variables (php, os) and added new build-time metadata (BUILD_TIMESTAMP).

Tagging and metadata enhancements:

• Added steps to generate a build timestamp and prepare image metadata, including logic to create branch- and matrix-specific tag prefixes and to determine which build is responsible for the latest tags.
• Refactored the Docker tag generation to produce more granular and descriptive tags, including OS-specific, PHP-specific, timestamped, and branch-prefixed tags, and consolidated tag assignment into a single step. [1] [2]

Workflow flexibility:

• Improved workflow triggers and scheduling, and cleaned up commented-out configuration for better maintainability.Updated GitHub Actions workflow to include scheduling and improved tag handling.