feat(cli, service): support for project image

[mohammad-alisafaee]

Description

Adds -i and --image flags to init and project edit commands that accepts a path/URL to an image. The image is copied to .renku/images/project/0.png and added to the project.

NOTE

• The image is always saved with a PNG extension; this shouldn't matter since UI loads the image correctly regardless (tested with dataset images).
• We don't allow adding non-image files from the local filesystem

Fixes #3576

[coveralls]

Pull Request Test Coverage Report for Build 6407729967

• 199 of 209 (95.22%) changed or added relevant lines in 28 files are covered.
• No unchanged relevant lines lost coverage.
• Overall first build on 3576-project-icon at 85.798%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
renku/core/dataset/dataset.py	20	21	95.24%
renku/core/migration/m_0010__metadata_fixes.py	1	2	50.0%
renku/core/migration/utils/conversion.py	1	2	50.0%
renku/domain_model/image.py	22	23	95.65%
renku/core/project.py	29	31	93.55%
renku/ui/cli/project.py	13	17	76.47%

Totals
Change from base Build 6407170776:	85.8%
Covered Lines:	26007
Relevant Lines:	30312

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💛 - Coveralls

[Panaetius]

looks great, tiny suggestion, feel free to ignore