This enables JavaScripts projects to have live previews straight in the
browser without requiring any local configuration. This uses the
CodeSandbox package `sandpack` to compile it all inside of an iframe.

This feature is off by default and can be toggled on in the admin
settings. Only projects with a `package.json` and a `main` key are
supported.

Updates happen in real-time with hot-reloading. We just watch for
changes to files and then send them to `sandpack` to allow it to reload
the iframe. The iframe includes a very simple navigation bar, the text
bar is `readonly` to stop users navigating away from the preview and
the back and forward buttons just pop/splice the navigation stack
which is tracked by a listener on `sandpack`

There is a button inside the iframe which allows the user to open the
projects inside of CodeSandbox. This button is only visible on
**public** projects. On private or internal projects this button
get hidden to protect private code being leaked into an external
public URL.

Closes #47268

Signed-off-by: NRémy Coutable <remy@rymai.me>

When a user checks the `accept` checkbox, we will track that
acceptance as usual. That way they don't need to accept again after
they complete the registration.

When an unauthenticated user visits the `/-/users/terms` page, there
is no button to accept, decline or continue. The 'current-user menu'
is also hidden from the top bar.

Adds changelog entry, changes RemoteMirror#sync? to be semantically sound and remove reference to pull mirrors in view

This enforces the terms in the web application. These cases are
specced:

- Logging in: When terms are enforced, and a user logs in that has not
  accepted the terms, they are presented with the screen. They get
  directed to their customized root path afterwards.
- Signing up: After signing up, the first screen the user is presented
  with the screen to accept the terms. After they accept they are
  directed to the dashboard.
- While a session is active:
  - For a GET: The user will be directed to the terms page first,
    after they accept the terms, they will be directed to the page
    they were going to
  - For any other request: They are directed to the terms, after they
    accept the terms, they are directed back to the page they came
    from to retry the request. Any information entered would be
    persisted in localstorage and available on the page.

This allows admins to define terms in the application settings.

Every time the terms are adjusted, a new version is stored and becomes
the 'active' version. This allows tracking which specific version was
accepted by a user.

Signed-off-by: NRémy Coutable <remy@rymai.me>

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Also reorganize application settings related to repository in more maninful sections
Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

* Replace btn-save with btn-success
* Add id to each section so it can be directly linked
Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

To make design consistent with project settings

Next admin area application settings are afected by this commit:

* Visibility and access control
* Account and limit settings
* Sign in
* Sign up
* Help page
* Pages
Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

`breadcrumb_title` is then overriden when needed

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>