Add pipeline for testing GitLab with SHA256 repositories
As of gitlab-org/gitlab!139108 (merged) we have the ability to create repositories using SHA256 object formats during project creations.
As per discussion in gitlab-org/gitlab#456530 (comment 1880785681) it would be useful to have the ability to run a scheduled/on-demand pipeline that would trigger the E2E test suite to determine if the use of the SHA256 introduces any breakages into the main GitLab application.
Proposal would be to modify the E2Es Project creation logic to enable the use of the the SHA256 experimental feature when a specific ENV is set in the pipeline, and allow for this job to be triggered by the gitaly project pipeline on demand.
Further Reading: https://about.gitlab.com/blog/2023/08/28/sha256-support-in-gitaly/