refactor: move checksum calculation to utils

[h0lyalg0rithm]

Proposed changes

Move sha256 calculation to utils.go file. Add tests to validate change

Types of changes

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• [ ] New feature (non-breaking change which adds functionality)
• [ ] Bugfix (non-breaking change which fixes an issue)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation Update (if none of the other choices applies)

Checklist

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• [x] I have signed the commit for DCO to be passed.
• [x] Lint and unit tests pass locally with my changes
• [x] I have added tests that prove my fix is effective or that my feature works (if appropriate)
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[glimchb]

@h0lyalg0rithm in a separate PR , not here, wdyt to move downloadAndValidateImage(), copyConfigurationFile(), launchScriptsConfiguration() to a new file... ? it looks not belonging to daemon.go

[h0lyalg0rithm]

@h0lyalg0rithm in a separate PR , not here, wdyt to move downloadAndValidateImage(), copyConfigurationFile(), launchScriptsConfiguration() to a new file... ? it looks not belonging to daemon.go

I think we should update the golinter version as it displays the line with the issue in the github action run.Here is the output https://github.com/h0lyalg0rithm/sztp/actions/runs/10222129019/job/28286107496

[h0lyalg0rithm]

@h0lyalg0rithm in a separate PR , not here, wdyt to move downloadAndValidateImage(), copyConfigurationFile(), launchScriptsConfiguration() to a new file... ? it looks not belonging to daemon.go

Yes it makes sense to move them

[glimchb]

I think we should update the golinter version

sure, go for it