metastore: skip checkpoint log when beginning

This log is written on every partition, even when there's no data loss.

The position.cmp(&delta_position.from) comparison doesn't account for
Position::Beginning being not equal to Position::offset(0u64). However logically
speaking moving from Beginning to 0u64 doesn't indicate any data loss -

  Position::Beginning means that no data was processed, and Position::offset(0)
  means offset 0 was processed.

I have run 'test_process_existing_messages' at
  quickwit/quickwit-indexing/src/source/queue_sources/coordinator.rs
and confirmed that the delta is -
  SourceCheckpointDelta[Position::offset(0)..Position::eof(file_len)]
and not -
  SourceCheckpointDelta[Position::Beginning..Position::eof(file_len)]

Author: noam-sol

quickwit/quickwit-metastore/src/checkpoint.rs

@@ -293,7 +293,11 @@ impl SourceCheckpoint {
             match position.cmp(&delta_position.from) {
                 Ordering::Equal => {}
                 Ordering::Less => {
-                    warn!(cur_pos=?position, delta_pos_from=?delta_position.from,partition=?delta_partition, "some positions were skipped");
+                    if !(position == Position::Beginning
+                        && delta_position.from == Position::offset(0u64))
+                    {
+                        warn!(cur_pos=?position, delta_pos_from=?delta_position.from,partition=?delta_partition, "some positions were skipped");
+                    }
                 }
                 Ordering::Greater => {
                     return Err(IncompatibleCheckpointDelta {