Add support for indirect template + customizations

[freddydk]

Changes included in this PR:

• Support indirect template repository = Point to an existing AL-Go repository as a template, like:

In this case, org/myptetemplate is a standard AL-Go repository, which gets updated as any other AL-Go repository using Update AL-Go System Files. This is a way of standardizing your repository based on type specific AL-Go templates (which can be private or public).

Normally, Update AL-Go System Files follows this mechanism:

Workflows and scripts are read from the template repository and modified based on settings and saved to the repository.

Using an indirect template repository, the picture looks like this:

Workflows and scripts are read from the "real" template repository and modified based on settings. Customizations for workflows in the indirect template repository are applied.

New workflows and scripts from the indirect template repository are copied over and new settings (for repo and for project) are copied over (if they don't already exist in the corresponding settings file).

The final repository can also contain customizations to workflows and the winner here is the indirect template repository (if a custom job or custom step exists in both places).

This PR: freddydk/customized#17 - is an example of a repository with customizations of CI/CD and _BuildALGoProject, which runs Update AL-Go System Files and gets customizations from the indirect template repository (both settings, scripts and workflow customizations)

TODO:

• End 2 End tests
• Unit tests
• Documentation

Documentation on customization capabilities is here: https://github.com/freddydk/AL-Go/blob/customize/Scenarios/CustomizingALGoForGitHub.md

[mortenseifert]

@freddydk, do you have an estimated time of completion for this PR? We've been testing it for a while and are considering deploying it live. However, we're a bit cautious about when the PR will be finalized and whether it will disrupt any modifications we've implemented.