fix: ignore blank initialBuckets entries during startup

[afranken]

Description

Rebased branch from #3071 onto main.

Related Issue

N/A

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[Copilot]

Pull request overview

This PR fixes a startup edge case where initialBuckets containing blank entries (e.g., [""]) could trigger creation of an invalid persisted bucket at the storage root, leading to bad state after restart.

Changes:

• Filter out blank/whitespace-only initialBuckets entries during bucket store initialization.
• Add a regression test asserting that blank initialBuckets does not create buckets or write files to the root store directory.
• Document the fix in CHANGELOG.md.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
server/src/main/kotlin/com/adobe/testing/s3mock/store/StoreConfiguration.kt	Filters blank initialBuckets entries before attempting bucket creation.
server/src/test/kotlin/com/adobe/testing/s3mock/store/StoreConfigurationTest.kt	Adds regression test for initialBuckets = listOf(\"\").
CHANGELOG.md	Notes the bug fix in the planned release section.

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