Release 14.6.0

See merge request gitlab-org/gitlab-shell!643

- Exclude Gitaly unavailable error from error rate !641
- Downgrade auth EOF messages from warning to debug !641
- Display constistently in gitlab-sshd and gitlab-shell !641
- Downgrade host key mismatch messages from warning to debug !639
- Introduce a GitLab-SSHD server version during handshake !640
- Narrow supported kex algorithms !638

Exclude Gitaly unavailable error from error rate

See merge request gitlab-org/gitlab-shell!641

The errors happen when a client closes a connection on handshake
They can be ignored to avoid noise

When a user hits repository rate limit, Gitaly returns an error
that the request can't be handled (Gitaly unavailable)

We should avoid this error to avoid exceeding the error rate

- Use console package to format the errors in gitlab-sshd
- Suppress internal Gitaly errors in client output

Downgrade host key mismatch messages from warning to debug

See merge request gitlab-org/gitlab-shell!639

Introduce a GitLab-SSHD server version during handshake

See merge request gitlab-org/gitlab-shell!640

This message doesn't provide that much value, so let's just drop it.