Add support for custom templates + customizations

[freddydk]

Changes included in this PR:

• Support custom 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:

File Type	Repository file(s)	AL-Go Template
Workflows	.github/workflows/*.yaml	<-
Repo Scripts	.github/*.ps1	<-
Project Scripts	.AL-Go/*.ps1	<-

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

Using a custom template repository, the picture looks like this:

File Type	Repository file(s)	Custom Template	AL-Go Template
Workflows	.github/workflows/*.yaml	<- Customizations	<-
Workflows	.github/workflows/*.yaml	<- New files
Repo Scripts	.github/*.ps1		<-
Repo Scripts	.github/*.ps1	<- New files
Repo Settings	.github/templateRepoSettings.doNotEdit.json	<- .github/AL-Go-Settings.json
Project Scripts	.AL-Go/*.ps1		<-
Project Scripts	.AL-Go/*.ps1	<- New files
Project Settings	.github/templateProjectSettings.doNotEdit.json	<- .AL-Go/settings.json

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

New workflows and scripts from the custom template repository are copied over.

Repo and Project settings from the custom template repository are copied over to new settings files, which are applied before the final repos repo and project settings in order to allow the indirect template to add new defaults to settings to be applied to all repositories.

The final repository can also contain customizations to workflows and the winner here is the indirect template repository (if a custom job 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)

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.

[freddydk]

Check #1097 - to ensure the scenario is supported