There is a PR to move checkpoint metrics out from transaction WT-11171 Better metrics for checkpoint, however t2 does not adjust this so all checkpoint stats are currently under UNKNOWN section.

This ticket is to:
1. Add a new section checkpoint to t2.
2. Add checkpoint metric to the new section and to WT Checkpoint view. (Don't remove the existing transaction checkpoint metric as it will be used in old mongodb versions.)
3. Add tooltips to checkpoint metrics if necessary.