Certain reverse proxies can send invalid IP addresses in the X-Forwarded-For header
For example, Apache can send (null).

Closes #20194

Storage path are not created until `TestEnv.init`, so we must skip
their validation on initialization.

Make Rack::Request use our trusted proxies when filtering IP addresses

## What does this MR do?

This allows us to control the trusted proxies while deployed in a private network.

## Are there points in the code the reviewer needs to double check?

If we want to limit what is impacted, we can do this specifically for the rack_attack request object.

## Why was this MR needed?

Normally Rack::Request will trust all private IPs as trusted proxies, which can cause problems if your users are connection on you network via private IP ranges.
    
Normally in a rails app this is handled by action_dispatch request, but rack_attack is specifically using the Rack::Request object instead.

## What are the relevant issue numbers?

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/17550

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- [ ] ~~API support added~~
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)


\cc @stanhu

See merge request !4958

This allows us to control the trusted proxies while deployed in a private network. Normally Rack::Request will trust all private IPs as trusted proxies, which can caue problems if your users are connection on you network via private IP ranges.

Normally in a rails app this is handled by action_dispatch request, but rack_attack is specifically using the Rack::Request object instead.

Each test reloads the trusted_proxies initializer, which in turn will set Rails.application.config.action_dispatch.trusted_proxies to something new. This will leak into the other tests, but the middleware that it is used in has already been loaded for the whole test suite, so it should have no impact.