metastore: skip logging checkpoint on position::beginning

[noam-sol]

Description

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.

How was this PR tested?

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)]

[guilload]

This is not the right fix. It's a bug in the checkpoint delta logic in the source. If you print the batch checkpoint deltas in that unit test, you will see something like:

for batch in batches {
            println!("batch checkpoint delta: {:?}", batch.checkpoint_delta);
        }

batch checkpoint delta: ∆(file:///var/folders/cj/3nfybfc572b9s2qvd18qzh_m0000gp/T/.tmpDz99t1:(00000000000000000000..~00000000000000000350])
batch checkpoint delta: ∆(file:///var/folders/cj/3nfybfc572b9s2qvd18qzh_m0000gp/T/.tmp6o6nbz:(00000000000000000070..~00000000000000000350])

The first checkpoint delta should be (beginning..~00000000000000000350].

Do you want to take a stab at it?