Handle race condition in Apply Registration to image task better

[jluethi]

@adrtsc I'm proposing a fix here for https://github.com/fractal-analytics-platform/fractal-tasks-core/issues/516 that introduces a max_retries parameter. I set it to 20, but we can of course tune that parameter further if needed.

closes #516

Checklist before merging

• [x] I added an appropriate entry to CHANGELOG.md

[github-actions[bot]]

Coverage report

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File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
fractal_tasks_core/tasks
apply_registration_to_image.py					221-227
Project Total

This report was generated by python-coverage-comment-action

[jluethi]

What we are missing in coverage here is reproducing a race time conflict during the tests. Given that it's a workaround, I'm fine with not having this included in our tests.

[adrtsc]

Looks good to me!