fix(cli): ssh setup and key usage

[olevski]

closes #3585
closes #3584

I am not sure that getting into people's ssh configurations to such extent (as we currently do) is maintainable and feasible without a lot of edge cases or bugs. So I decided to simply give a warning when the renku session ssh-setup command is used. When I saw this command (including other users from discord) I expected that it would inject ssh keys into the current project. But it does not do this. It only generates/updates stuff in ~/.ssh/renku.

I think a more sustainable solution is to step back from doing all this ssh configuration manipulation for users. Because the biggest problem is that it is hard to make things work both with and without using the renku CLI. But we can discuss this further in a separate issue.

[coveralls]

Pull Request Test Coverage Report for Build 6310115018

• 2 of 2 (100.0%) changed or added relevant lines in 2 files are covered.
• 54 unchanged lines in 13 files lost coverage.
• Overall coverage increased (+1.0%) to 86.766%

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Files with Coverage Reduction	New Missed Lines	%
renku/core/dataset/providers/dataverse.py	1	88.86%
renku/core/migration/m_0003__1_jsonld.py	1	87.68%
renku/core/util/requests.py	1	94.69%
renku/core/util/tabulate.py	1	96.3%
renku/core/workflow/activity.py	1	93.93%
renku/ui/cli/init.py	1	96.9%
renku/ui/service/cache/models/file.py	1	93.15%
renku/command/rollback.py	2	78.7%
renku/core/util/os.py	2	88.38%
renku/ui/service/jobs/cleanup.py	2	80.65%

Totals
Change from base Build 6049920186:	1.0%
Covered Lines:	26167
Relevant Lines:	30158

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💛 - Coveralls

[m-alisafaee]

Thanks Tasko! I've just added 2 comments regarding a message formatting/wording.