exp show: Add option to filter out checkpoints

[daavoo]

If multiple experiments with checkpoints are run, the table can get quickly populated with too many rows.

It would be nice to have an option to filter out intermediate checkpoints, leaving only a single row per experiment.

For example from:

Experiment	Created	step	loss	accuracy
workspace	-	9	0.13434	0.94875
main	Sep 14, 2021	-	-	-
│ ╓ 54bdc11 [exp-76ba1]	06:16 PM	9	0.13434	0.94875
│ ╟ 0d15982	06:16 PM	9	0.13434	0.94875
│ ╟ 0221f75	06:16 PM	8	0.14528	0.94422
│ ╟ 3c919ce	06:16 PM	7	0.16	0.93915
│ ╟ f8614f3	06:15 PM	6	0.16907	0.93625
│ ╟ 145cf38	06:15 PM	5	0.18693	0.93032
│ ╟ 1380f6b	06:15 PM	4	0.20545	0.92323
│ ╟ 2c261e6	06:15 PM	3	0.22706	0.9165
│ ╟ 474aab2	06:15 PM	2	0.25087	0.90902
│ ╟ 8574046	06:15 PM	1	0.29243	0.89367
├─╨ 89c129f	06:14 PM	0	0.43671	0.8438
│ ╓ 2e3c654 [exp-12afc]	06:14 PM	9	0.18331	0.92932
│ ╟ ceee9e6	06:13 PM	9	0.18331	0.92932
│ ╟ 92fa0de	06:13 PM	8	0.19382	0.92642
│ ╟ 20d54e5	06:13 PM	7	0.20558	0.92147
│ ╟ 1a98b62	06:13 PM	6	0.21462	0.91743
│ ╟ e3f5963	06:13 PM	5	0.23029	0.9131
│ ╟ 4ddaa64	06:13 PM	4	0.24762	0.90817
│ ╟ 6f2cbd7	06:12 PM	3	0.26551	0.90218
│ ╟ 0f3f2bd	06:12 PM	2	0.29	0.89392
│ ╟ a769a16	06:12 PM	1	0.33083	0.8808
├─╨ ee36d3a	06:12 PM	0	0.48448	0.82805

To:

Experiment	Created	step	loss	accuracy
workspace	-	9	0.13434	0.94875
main	Sep 14, 2021	-	-	-
54bdc11 [exp-76ba1]	06:16 PM	9	0.13434	0.94875
2e3c654 [exp-12afc]	06:14 PM	9	0.18331	0.92932

[dberenbaum]

Related: #6194