[backup] Log upload endpoint

Summary:
ENG-5329 : Add endpoints for uploading a log

Add the actual logic for uploading a log

Depends on D10453

Test Plan:

• Modify the maximum size that we can keep in dynamodb to 200
• Upload two logs:

UploadLogRequest {
  log_id: 11111,
  content: vec![1; 10],
  attachments: None,
}
UploadLogRequest {
  log_id: 22222,
  content: vec![2; 10000],
  attachments: Some(vec!["attachment".into()]),
}

• Checked that I got two upload respones
• Checked the db:
  • 11111 has content column with bytes
  • 22222 has attachments column with one BlobInfo and blobInfo column with a BlobInfo for content
• Checked blob logs:
  • "Assign holder request" for hash "attachment"
  • Assign holder request and "Upload blob request" for content of the second request

Reviewers: bartek, kamil

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10456