terragrunt generation: gitroot not prepended to digger project

[motatoes]

Bug fix for: gitRoot parameter doesn’t map to the right path with discovered projects because it only uses the initial terragrunt.hcl as the root of directory, we need to prepend the gitRoot parameter in this case.

Example in this folder structure:

# tree
| - cloud
|.       - projectA
|.       - projectB
|.       - projectC
|.       - projectDTerragrunt
|.              - prod
|.              - nonprod

# digger.yml
generate_projects:
  terragrunt_parsing:
    parallel: true
    createProjectName: true
    createWorkspace: false
    defaultWorkflow: gcp_terragrunt
    ignoreDependencyBlocks: false
    ignoreParentTerragrunt: false
    gitRoot: cloud/projectDTerragrunt

The corresponding digger projects generated are: prod/ and nonprod. Whereas they should have been: cloud/projectDTerragrunt/prod and cloud/projectDTerragrunt/nonprod

In this fix we check for the existense of a gitRoot parameter and prepend it to generated digger projects.

Tested to fix in: https://github.com/diggerhq/demo-terragrunt-backendless-nested/actions/runs/8419854091