Github App Authentication Support

# Summary

for github artifacts would be nice to support github app authentication , as it simple to manage access to repositories than using personal access token.

What change needs making?

Implement github jwt authentication for application in workflow/artifacts/git/git.go , "github.com/bradleyfalzon/ghinstallation" is suppose to provide the helpers to do it simply, also new parameters to the 'git' artifact will be needed as 'Private Pem Key', 'Application Id' and 'Installation Id'

# Use Cases
When manage a huge number of repos from different teams is simpler to use github app to allow access from the workflow or CI/CD platform to the repos than using Personal Access Tokens, this way , is less human interaction needed

When would you use this?

to checkout code from private github repos
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**Message from the maintainers**:

Impacted by this bug? Give it a 👍. We prioritise the issues with the most 👍.

Start in workflow/artifacts/git/git.go and review how the git artifact currently authenticates to GitHub repositories. Check the ghinstallation helper and determine how Private Pem Key, Application Id, and Installation Id fit the artifact parameters; done means a workflow can use GitHub App JWT authentication to check out private GitHub repositories.

Written by the indexing model from the issue text.