After moving the multiproc dir cleanup into `config.ru`:`warmup`, we
stopped cleaning Sidekiq metrics dir which is not correct.
This MR intended to fix that. More details:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/31668

When we hit our app with the initial request, in `warmup`,
some metrics already being created as well as corresponding files.
If we do `multiproc_file_dir` cleanup after that, we delete the files
from the dir while keeping them in memory which leads to the incorrect
behavior: the metric is being updated in in-memory, while is not present
in the db, not sent to Prometheus as the result.

This update has two important fixes:

1. It reverts the monkey patch introduced in
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/23385 since
https://github.com/rack/rack/pull/1201 is now part of the release.

2. Preserve forwarded IP address for trusted proxy chains
(https://github.com/rack/rack/pull/1343).

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

Rack with Unicorn is unable to handle chunked requests due to private `eof?` method.
This exposes `eof?` not changing `rack` behavior.

Issue: https://gitlab.com/gitlab-org/gitlab-ee/issues/8539

These limits were updated in our docs, and in omnibus some time ago. But
the defaults in the source-install were missed.

after the request. This way, we could release the
project referred from the controller, which potentially
referred a repository which potentially allocated a lot of
memories.

Before this change, we could hold the last request data
and cannot release the memory. After this change, the
largest request data should be able to be collected from GC.

This might not impact the instances having heavy load,
as the last request should be changing all the time,
and GC won't kick in for each request anyway.

However it could still potentially allow us to free more
memories for each GC runs, because now we could free one
more request anyway.