Signed-off-by: Takuya Noguchi <takninnovationresearch@gmail.com>

This allows us (and others) to test drive Puma without it affecting all
users. Puma can be enabled by setting the environment variable
"EXPERIMENTAL_PUMA" to a non empty value.

It looks like gRPC may have worked around
https://github.com/google/protobuf/issues/4210 via
https://github.com/grpc/grpc/pull/14634.

This is needed to support Ruby 2.5
(https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/22555).

Remove gitlab-grit as a transitive dependency of GitLab

Closes #44361

See merge request gitlab-org/gitlab-ce!22373

Use grpc v1.15.x

See merge request gitlab-org/gitlab-ce!22350

Removing this dependency also allows us to remove a transitive
dependency on gitlab_grit - which is the whole point of this exercise.

I don't think we can EOL gitlab_grit until it's removed as a dependency
from gitaly-ruby, but this at least gets it out of gitlab-ce.

This allows us to avoid one transitive dependency on gitlab-grit. The
aim is to remove all transitive dependencies.

This saves about 128 MB of baseline RAM usage per Unicorn and
Sidekiq process (!).

Linguist wasn't detecting languages anymore from CE/EE since
9ae8b57467ac8b38f1fa9020a466d94a93cbb9dd. However, Linguist::BlobHelper
was still being depended on by BlobLike and others.

This removes the Linguist gem, given it isn't required anymore.
EscapeUtils were pulled in as dependency, but given Banzai depends on
it, it is now added explicitly.

Previously, Linguist was used to detect the best ACE mode. Instead,
we rely on ACE to guess the best mode based on the file extension.

Add reliable sidekiq fetcher

See merge request gitlab-org/gitlab-ce!21715