Add Loglevel configuration for gitlab-sshd implementation of gitlab-shell
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### Description
Hello, when using the gitlab-sshd implementation of gitlab-shell there is no possibility to set the loglevel to e.g. WARN or ERROR. This is only possible when using the default implementation for gitlab-shell (OpenSSH). However only gitlab-sshd provides the option of exposing metrics. In our case setting the log level is necessary because the gitlab-shell pod logs on average per day 20 million log entries. We can workaround this by filtering logs at the Logging API, but this is a rather coarse grained measure.
### Proposal
Please enable the possibility of setting a certain log level of the gitlab-sshd implementation.
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