Replace openssh with openssh-server

[BrBrRoman]

We don't need openssh-client.
It will allow to save around 3.2 megabytes from the final image.
I have tested cloning and pushing the change to the repository and everything functioned correctly.

[techknowlogick]

Some users use ssh client in git hooks to push to other mirrors. This would be a breaking change

[codecov-io]

Codecov Report

Merging #6162 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #6162      +/-   ##
==========================================
- Coverage   38.84%   38.83%   -0.02%     
==========================================
  Files         354      354              
  Lines       50177    50177              
==========================================
- Hits        19493    19487       -6     
- Misses      27859    27865       +6     
  Partials     2825     2825

Impacted Files	Coverage Δ
models/repo_list.go	66.84% <0%> (-1.06%)	⬇️
routers/repo/view.go	41.08% <0%> (-1%)	⬇️

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