feat(service): accept commit SHA in read endpoints

[olevski]

closes #3579

/deploy #persist

This is ready for review.

[RenkuBot]

You can access the deployment of this PR at https://renku-ci-rp-3608.dev.renku.ch

[coveralls]

Pull Request Test Coverage Report for Build 6549700209

• 37 of 45 (82.22%) changed or added relevant lines in 10 files are covered.
• 1007 unchanged lines in 82 files lost coverage.
• Overall coverage decreased (-3.3%) to 82.91%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
renku/core/util/git.py	7	9	77.78%
renku/ui/service/gateways/repository_cache.py	0	6	0.0%

Files with Coverage Reduction	New Missed Lines	%
renku/core/dataset/providers/dataverse.py	1	88.86%
renku/core/dataset/providers/renku.py	1	89.76%
renku/core/image.py	1	97.14%
renku/core/migration/m_0003__1_jsonld.py	1	87.68%
renku/core/workflow/activity.py	1	93.29%
renku/domain_model/dataset.py	1	93.3%
renku/domain_model/provenance/agent.py	1	81.72%
renku/domain_model/template.py	1	90.43%
renku/ui/cli/init.py	1	96.9%
renku/ui/cli/service.py	1	28.57%

Totals
Change from base Build 6544141496:	-3.3%
Covered Lines:	25469
Relevant Lines:	30719

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💛 - Coveralls