Add UI to support SHA256 repositories creation

What does this MR do and why?

Contributes to #426803 (closed)

Problem

Gitaly provides a support for SHA256 repositories. But this feature is not supported by Rails application.

Solution

Add UI to allow users to create new projects with SHA256 repositories.

Screenshots or screen recordings

How to set up and validate locally

1. Enable feature flag Feature.enable(:support_sha256_repositories)

2. Visit create new project page (http://127.0.0.1:3000/projects/new)

3. Select Create blank project

4. Check Use SHA-256 for repository hashing algorithm checkbox

5. Provide project name and group

6. Click Create project button

7. The project should be successfully created

8. Copy the last commit hash

9. It should have 64 characters (for SHA256)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.