Replace Jenkins with GitHub Action Workflow for New Build System

[ric394]

Describe the new feature

To improve continuous integration and development of APSIM GitHub Actions will be utilised. Currently Jenkins is utilised for this purpose.
GitHub Actions is tightly integrated into the repository and utilising this service simplifies maintenance and improves observability of workflows.

The current CI/CD functions that Jenkins provides will be covered by GitHub Actions. These include:

• testing
• distributing model validation runs
• building of APSIMX releases
• building and uploading of various docker images

Note: The development of these workflows will not interrupt the normal processes covered by Jenkins and will be developed concurrently until the new process is ready to replace Jenkins.