Add support for gotestsum

This MR adds support for https://github.com/gotestyourself/gotestsum by adding make test_fancy and make test_golang_fancy:

$ make test_golang_fancy
∅  client/testserver
∅  cmd/check
∅  cmd/gitlab-shell
∅  cmd/gitlab-shell-authorized-keys-check
∅  cmd/gitlab-shell-authorized-principals-check
✓  cmd/check/command (446ms)
✓  cmd/gitlab-shell/command (589ms)
✓  cmd/gitlab-shell-authorized-keys-check/command (327ms)
✓  client (795ms)
✓  cmd/gitlab-shell-authorized-principals-check/command (400ms)
∅  internal/command/commandargs
✓  internal/command (511ms)
✓  internal/command/authorizedprincipals (613ms)
✓  internal/command/githttp (733ms)
✓  cmd/gitlab-sshd (801ms)
∅  internal/command/readwriter
✓  internal/command/lfsauthenticate (307ms)
∅  internal/command/shared/disallowedcommand
✓  internal/command/receivepack (334ms)
✓  internal/command/shared/accessverifier (384ms)
✓  internal/command/shared/customaction (305ms)
✓  internal/command/uploadarchive (404ms)
✓  internal/command/uploadpack (416ms)
✓  internal/config (328ms)
✓  internal/console (122ms)
✓  internal/executable (121ms)
∅  internal/gitlabnet
✓  internal/gitaly (356ms)
✓  internal/command/authorizedkeys (3.327s)
✓  internal/gitlabnet/accessverifier (352ms)
✓  internal/gitlabnet/authorizedkeys (331ms)
✓  internal/command/discover (3.849s)
✓  internal/command/healthcheck (3.552s)
✓  internal/gitlabnet/discover (317ms)
✓  internal/gitlabnet/git (379ms)
✓  internal/gitlabnet/healthcheck (354ms)
✓  internal/command/personalaccesstoken (3.307s)
✓  internal/gitlabnet/personalaccesstoken (395ms)
∅  internal/metrics
✓  internal/gitlabnet/twofactorrecover (400ms)
✓  internal/gitlabnet/twofactorverify (417ms)
✓  internal/command/twofactorrecover (3.317s)
✓  internal/handler (410ms)
✓  internal/keyline (395ms)
✓  internal/logger (428ms)
✓  internal/pktline (365ms)
✓  internal/command/twofactorverify (3.315s)
∅  internal/testhelper
∅  internal/testhelper/requesthandlers
✓  internal/sshenv (276ms)
✓  internal/gitlabnet/lfsauthenticate (3.351s)
✓  internal/sshd (4.085s)

=== Skipped
=== SKIP: cmd/gitlab-sshd TestGitReceivePackSuccess (0.00s)
    acceptance_test.go:76: GITALY_CONNECTION_INFO is not set

=== SKIP: cmd/gitlab-sshd TestGeoGitReceivePackSuccess (0.00s)
    acceptance_test.go:76: GITALY_CONNECTION_INFO is not set

=== SKIP: cmd/gitlab-sshd TestGitUploadPackSuccess (0.00s)
    acceptance_test.go:76: GITALY_CONNECTION_INFO is not set

=== SKIP: cmd/gitlab-sshd TestGitUploadArchiveSuccess (0.00s)
    acceptance_test.go:76: GITALY_CONNECTION_INFO is not set

DONE 477 tests, 4 skipped in 13.371s

The benefits are a nicer, easier to read test output that is also sent to cover.xml in the JUnit XML format which we can leverage using https://docs.gitlab.com/ee/ci/testing/unit_test_reports.html#how-to-set-it-up.