sync-diff-inspector: support skipping validation for tables that don't exist upstream or downstream

[liumengya94]

Feature Request

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

The tool cannot be used in some scenarios: if the number of tables on the two clusters is different.
for example #680

Describe the feature you'd like:

Record and skip the tables that exist only upstream or downstream, and continue validating the remaining tables until the task is completed. And print information about the skipped table in progress and summary.

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy: