Fix MissingBlobException after migration to S3

After trying to migrate to S3 following https://blog.sonatype.com/dynamic-storage-improvements-3.15 , it is now not possible to download or publish artifacts. Server raises HTTP 500 MissingBlobException.

The main issue seems to be

org.sonatype.nexus.repository.storage.MissingBlobException: Blob default@D2916B09-C561F73C-04C6B773-FEE88C9F-082B2630:dd7af10c-00dd-45d0-8be1-ad1d4d111639 exists in metadata, but is missing from the blobstore

It looks like https://issues.sonatype.org/browse/NEXUS-15095 fixed in 3.15.0 but we're on Nexus PRO 3.15.2-01.

The server logs are full of

• UNKNOWN org.sonatype.nexus.repository.storage.StorageTxImpl - Reached max retries: 8/8
• UNKNOWN org.sonatype.nexus.repository.npm.internal.NpmProxyFacetImpl - Unable to find blob default@D2916B09-C561F73C-04C6B773-FEE88C9F-082B2630:fdd50d9f-247a-44ab-8669-f60fdaf2d211
• UNKNOWN org.sonatype.nexus.repository.httpbridge.internal.ViewServlet - Failure servicing: GET (...)
  org.sonatype.nexus.repository.storage.MissingBlobException: Blob (...) exists in metadata, but is missing from the blobstore