[e2e] [ENHANCEMENT] Allow adding Checksum when creating a new Image from URL

[harvesterhci-io-github-bot]

What's the test to develop? Please describe

See harvester/dashboard#954 (comment)

Prerequisite and dependency of test

Any prerequisite environment and pre-condition required for this test.
Provide test case dependency here if any.

Describe the items of the test development (DoD, definition of done) you'd like

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• Add checksum to ubuntu image fixture
• Add checksum to image model
• Add test case for volume creation with image checksum
• Add negative test case for volume creation with incorrect checksum
• Add check for invalid checksum with assertion
• Refactor tests to add in docs/pydoc
• Add in opensuse checksum
• Add default checksum for opensuse and ubuntu based on default images
• Verify that no new tests are failing in images or volumes integration tests

Additional context

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related issue: harvester/harvester#5141