Function upsert_note_bytes_for 

pub fn upsert_note_bytes_for(
    git_dir: &Path,
    format: ObjectFormat,
    store: &FileRefStore,
    notes_ref: &NotesRef,
    annotated: &ObjectId,
    body: &[u8],
    message: &str,
    identity: &NotesCommitIdentity,
    ref_expected: Option<RefTarget>,
) -> Result<UpsertNoteOutcome>

Write body as a blob, then call upsert_note_for.