Add BYO FileStore UC2 receiver: Azure Blob SDK integration for SJP

[allanmckenzie]

Summary

• Upgrades service-parent-pom to 17.104.3 (required for Azure SDK versions in common-bom) and bumps project version to 17.104.1-SNAPSHOT
• Adds sjp-file-store module (sjp-file-store-core + sjp-file-store-test-utils) with Azure Blob Storage integration: FileStorer, FileRetriever, FileIngestor, SasUriGenerator, StoragePath, and dual-auth producer (BlobContainerClient via connection string or DefaultAzureCredential)
• Implements UC2 receiver: new sjp.ingest-file command endpoint (RAML, JSON schema, DRL access control, IngestFileApi, IngestFileCommandHandler) that uses FileIngestor to server-side-copy a blob from a SAS URI into SJP's internal Azure Blob container
• Wires PressAndTransparencyReportStrategy to dispatch sjp.ingest-file when sourceUri is present in the public.systemdocgenerator.events.document-available event payload (set by the companion SDG UC2 owner PR)

Test plan

• Unit tests pass for all new classes in sjp-file-store-core
• IngestFileCommandHandlerTest verifies correct delegation to FileIngestor
• IT tests (FileStorerIT, FileRetrieverIT, FileIngestorIT) pass against Azurite via mvn verify -Psjp-integration-test
• End-to-end: SDG generates a transparency report → document-available event carries sourceUri → SJP dispatches sjp.ingest-file → blob appears in SJP's internal/ container in Azurite

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