Respect log-level configuration again

Closes #502

See merge request gitlab-org/gitlab-shell!530

This was lost in the move from Ruby to Go. Restore it now.

Changelog: fixed

Only validate SSL cert file exists if a value is supplied

See merge request gitlab-org/gitlab-shell!527

This fixes a regression in
https://gitlab.com/gitlab-org/gitlab-shell/-/merge_requests/508. If an
HTTPS internal API URL were used, gitlab-shell would not work at all. We
now handle blank `caFile` properly.

Relates to https://gitlab.com/gitlab-org/gitlab-shell/-/issues/529

makefile: properly escape '$' in VERSION_STRING

See merge request gitlab-org/gitlab-shell!525

refactor: unify instantiation of command.Shell

Closes #517

See merge request gitlab-org/gitlab-shell!520

Improve err message given when Gitaly unavailable

Closes gitlab#340819

See merge request gitlab-org/gitlab-shell!526

If git is not available or gitlab-shell is not built in a repository, it falls back the VERSION file. That command is not properly escaped and results in the message:

> awk: cmd. line:1: Unexpected token

When you remove the `2>/dev/null`. Escape the '$' characters to solve this.

Add context fields to logging

See merge request gitlab-org/gitlab-shell!524

It adds correlation ids wherever possible

Extract server config related code out of sshd.go

Closes #523

See merge request gitlab-org/gitlab-shell!523

Unit test exit-codes for sshd/session.go

Closes #522

See merge request gitlab-org/gitlab-shell!522

Unit test sshd.handleEnv function

See merge request gitlab-org/gitlab-shell!521

Add TestInvalidClientConfig and TestNewServerWithoutHosts for sshd.go

See merge request gitlab-org/gitlab-shell!518

refactor: rearchitect command and executable Go modules

Closes #214

See merge request gitlab-org/gitlab-shell!514

Fix a flaky test

See merge request gitlab-org/gitlab-shell!519

Update Ruby version to 2.7.4 and add Go version 1.16.8 for tooling

See merge request gitlab-org/gitlab-shell!517

build: move build task to the top of the Makefile

See merge request gitlab-org/gitlab-shell!513

refactor: remove commandargs.GenericArgs

Closes #212

See merge request gitlab-org/gitlab-shell!506

parse logic will only run if the executable accept args.
healthcheck is the only one not accepting arguments.

refactor: move away from ioutil (deprecated)

See merge request gitlab-org/gitlab-shell!511

Release v13.21.0

See merge request gitlab-org/gitlab-shell!512