Add Slicer commit date as a comment along side the SHA

[jcfr]

The following code should be updated:

SlicerCustomAppTemplate/{{cookiecutter.project_name}}/CMakeLists.txt

Line 18 in 05e8429

GIT_TAG {% github_repo_branch_sha "Slicer/Slicer", "main" %}

To have the following:

Before:

 GIT_TAG        b0b9be57cb7d1a1e462143ec74e3d37d271d114d

After:

 GIT_TAG        b0b9be57cb7d1a1e462143ec74e3d37d271d114d  # 2023-03.04