Update docs structure Reference/GitHub

[DFriend01]

Purpose

GitHub is mostly used as part of our infrastructure, so we should move the content to a more appropriate location.

Changes

Move the GitHub page, both in the filesystem and in the website page structure. Remember to check for broken links that may result in moving this folder to a new location (mostly images in the GitHub folder and links to any workflow content).

Current Location: reference/github
New Location: reference/infrastructure/github

Updated Page Tree

nav:
  ...
- Reference:
    - reference/index.md
    ...
    - Infrastructure:
      - GitHub:
        - Development Workflow:
          - Overview:
            - reference/infrastructure/github/workflow/index.md
          - Creating Issues: reference/infrastructure/github/workflow/issues.md
          - Developing on Branches: reference/infrastructure/github/workflow/branches.md
          - Pull Requests: reference/infrastructure/github/workflow/pr.md
    ...

[patrick-5546]

Let's keep the page structure flat