It adds correlation ids wherever possible

Gitaly project now properly respects module release flow
and includes a module suffix in the package name. It requires
to re-write all non-suffixed imports with suffixed of a specific
version of tha module. With proper module versioning we don't
need to use a 'replace' directive to point to specific commit
and can use semantic versioning for the gitaly dependency.

Part of: https://gitlab.com/gitlab-org/gitaly/-/issues/3177

Previously, opentracing (if configured) was initialized late in the
gitlab-shell process's lifespan, coming just before making a gRPC
call to Gitaly.

By moving the opentracing initialization to be at process startup, we
make it available for the whole process lifecycle, which is very useful
to gitlab-sshd, as it means we'll only call tracing.Initialize() once
on process startup, rather than once per SSH connection.

To get this working, we need to introduce a context to gitlab-sshd.
This carries the client/service name, but also carries an initial
correlation ID. The main outcome of this is that all calls to the
authorized_keys endpoint from a given gitlab-sshd process will now
share a correlation ID. I don't have a strong opinion about this either
way.

Changelog: fixed

Respect parent context for Gitaly calls

See merge request gitlab-org/gitlab-shell!469

This behaviour dates from when Gitaly RPCs were executed in Ruby by a
Go subprocess. It's not needed for gitlab-shell now that it's in Go,
and it's a very strange thing for gitlab-sshd. Best just to remove it.

If we wanted to retain this behaviour, we could have an `os.Chdir` call
in the gitlab-shell binary, but I just don't think it's needed.

Changelog: fixed

Without these changes, Gitaly calls would not be linked to a parent
context. This means that they would have an unassociated correlationID,
and Gitaly RPC calls would not be cancel()ed by parent context
cancellation.

Changelog: fixed