This implements the last part of the AddAttachments endpoint - moving log item storage to blob service when it's too large.

Depends on D6206

1. Manually created large log item, ensured that it's slightly less than 400kb.
2. Called AddAttachments providing a long attachments holder string.
3. Ensured Blob service got called and the log was uploaded & database entity was updated.

The backup service integration tests cover this case, but this needs remaining endpoints to be implemented.