Improve usability: `tidb-lightning-ctl` print checkpoint status

[lance6716]

Feature Request

Is your feature request related to a problem? Please describe:

In some cases user may need to grep lightning's log and modify stalled checkpoint and importer's data directory, which needs lightning developer's help and confirm to perform actions on internal data.

Describe the feature you'd like:

tidb-lightning-ctl could show checkpoint status(with some explanation?) of each table, and help remove importer's engine files.

When importing task is running, user could have confidence to actively terminate importing task(to alter configuration or pause) by reading checkpoint status.

When importing task is not running, tidb-lightning-ctl may output stalled tables and their status in a more friendly way, to guide user copy-and-paste to clean or continue, to further reduce oncall.

Describe alternatives you've considered:

• interactive tidb-lightning-ctl
• print tidb-lightning-ctl --checkpoint-error-destroy=all when lightning found stalled checkpoint, another way to guide user.

Teachability, Documentation, Adoption, Optimization: