Add E2E test for git sha256 support

What does this MR do and why?

Add pipelines to help provide ongoing validation of the support for git's sha256 object format Part of Add pipeline for testing GitLab with SHA256 rep... (gitlab-org/quality/quality-engineering/team-tasks#2736 - closed)

Ideally I think we might want to leave this in only the nightly jobs in the longer term, but as there are a number of known issues that team members may want to directly address let's also allow for the job to be present in the regular master pipeline for now so it can be triggered during development work on-demand.

See: Allow Gitlab Rails to work with SHA256 reposito... (&10981) for further info about SHA256 support.

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

• The pipeline should require a manual trigger.

• At this moment in time, the jobs will fail. We have logged a series of issues around the initial set of known issues:

  • [Sha 256] Unable to add note to MR diff when us... (#463793 - closed)
  • [Sha 256] Project snippet repos should have the... (#463827)
  • [Sha 256] Project wiki repos should have the sa... (#463828)
  • Allow push-to-create repository functionality t... (#423318)
  • [Sha 256] unable to create sha256 repository vi... (#463857)
  • [Sha 256] Blame does not work when object forma... (#463860 - closed)