Update Gitlab Shell version to 14.6.0

- Exclude Gitaly unavailable error from error rate
- Downgrade auth EOF messages from warning to debug
- Display constistently in gitlab-sshd and gitlab-shell
- Downgrade host key mismatch messages from warning to debug
- Introduce a GitLab-SSHD server version during handshake
- Narrow supported kex algorithms

Changelog: changed

GITLAB_SHELL_VERSION

-14.5.0
+14.6.0