Add php-ssh container

This commit introduces a new PHP-SSH container. As part of this addition, updates have been made to the docker-compose.yml, Dockerfile under src, and build.yml under GitHub workflows. The docker-compose.yml now includes the php-ssh service configuration while the Dockerfile has been edited to install the openssl-sftp-server for the SSH service.

Update Docker tag prefix

Merge pull request #5 from sitepilot/add-php8.3

Add PHP 8.3

Update prefix syntax in GitHub Action image tags

This commit fixes the syntax of the prefix in the image tag definitions within our GitHub Actions. It ensures a hyphen occurs between the prefix and the PHP version, increasing readability and overall consistency across tags. Additionally, unique prefix adjustments were made for pull request (PR) events.