Fix URL for UI navigation to Create a new project with Git push docs

What does this MR do and why?

Updates the link in the UI from the Create a new project page that directs you to the Create a new project with Git push documentation section. Also updates the variable names and specs related to it.

Before	After
https://docs.gitlab.com/ee/user/project/working_with_projects.html#create-a-new-project-with-git-push	https://docs.gitlab.com/ee/user/project/index#create-a-new-project-with-git-push

URL change introduced by: !109152 (merged)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Visit the Create new project page
   • e.g. https://gitlab.com/projects/new
2. Click on the Show command button at the bottom of the page
3. Click on the What does this command do? within the modal