chore: Remove startup dependency on Sipi, remove checking iiif server available on startup

[seakayone]

• Do not fail if IIIF server is not available at startup

Pull Request Checklist

Task Description/Number

Issue Number: DEV-

PR Type

• build/chore: maintenance tasks (no production code change)
• docs: documentation changes (no production code change)
• feat: represents new features
• fix: represents bug fixes
• perf: performance improvements
• refactor: represents production code refactoring
• test: adding or refactoring tests (no production code change)
• deprecated: Deprecation warning (ideally referencing a migration guide)

Basic requirements for bug fixes and features

• Tests for the changes have been added
• Docs have been added / updated

Does this PR introduce a breaking change?

• Yes

Does this PR change client-test-data?

• Yes

[siers]

Are you implementing this because this is not a continual health-check, but a one-off instead?

[BalduinLandolt]

Great!

[seakayone]

Are you implementing this because this is not a continual health-check, but a one-off instead?

I don't think I would even want to have continuous health-check for Sipi. The dsp-api would mostly work without it; a minor set of functionality is of course degraded. Unlike if the database would be down, which is a far more crucial dependency.