Perform Git over HTTP request to primary repo

Instead of proxying the Geo request via Rails, let's do the Git over HTTP request to the primary repo

Related issue: #614 (closed)

sequenceDiagram
    participant C as Git on client
    participant S as GitLab Shell
    participant I as Workhorse & Rails
    participant P as Workhorse & Rails

    Note left of C: git fetch
    Note over S,I: Secondary site
    Note over P: Primary site
    C->>+S: ssh git receive-pack request
    S->>I: SSH key validation (api/v4/internal/authorized_keys?key=..)
    I-->>S: HTTP/1.1 300 (custom action status) with {endpoint, msg, primary_repo}
    S->>I: POST /api/v4/geo/proxy_git_ssh/info_refs_receive_pack
    I->>P: POST $PRIMARY/foo/bar.git/info/refs/?service=git-receive-pack
    P-->>I: HTTP/1.1 200 OK
    I-->>S: <response>
    S-->>C: return Git response from primary
    C-->>S: stream Git data to push
    S->>I: POST /api/v4/geo/proxy_git_ssh/receive_pack
    I->>P: POST $PRIMARY/foo/bar.git/git-receive-pack
    P-->>I: HTTP/1.1 200 OK
    I-->>S: <response>
    S-->>-C: gitlab-shell receive-pack response

After

When a user performs a Git over SSH request to secondary node, Gitlab Shell performs Git over HTTP requests to primary Workhorse & Rails.

sequenceDiagram
    participant C as Git on client
    participant S as GitLab Shell
    participant I as Workhorse & Rails
    participant P as Workhorse & Rails

    Note left of C: git fetch
    Note over S,I: Secondary site
    Note over P: Primary site
    C->>+S: ssh git receive-pack request
    S->>I: SSH key validation (api/v4/internal/authorized_keys?key=..)
    I-->>S: HTTP/1.1 300 (custom action status) with {endpoint, msg, primary_repo, authorization headers}
    S->>P: POST $PRIMARY/foo/bar.git/info/refs/?service=git-receive-pack
    P-->>S: HTTP/1.1 200 OK
    P-->>S: <response>
    S-->>C: return Git response from primary
    C-->>S: stream Git data to push
    S->>P: POST $PRIMARY/foo/bar.git/git-receive-pack
    P-->>S: HTTP/1.1 200 OK
    P-->>S: <response>
    S-->>-C: gitlab-shell receive-pack response

Testing

• Install Geo https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/main/doc/howto/geo.md
• Checkout to Geo: Send auth headers to GitLab Shell (gitlab!111888 - merged) on Gitlab Rails secondary
• Checkout to this branch on Gitlab Shell secondary
• gdk start
• gdk stop sshd (in order to run it manually to make sure it compiles and outputs logs)
• make && bin/gitlab-sshd -config-dir=. from Gitlab Shell
• Perform push to secondary
• Gitlab Shell logs should show that the requests go to geo/proxy_git_ssh/... endpoints
• Enable geo_proxy_direct_to_primary feature flag on Rails
• Perform push to secondary
• Gitlab Shell logs should show that Primary is requested directly