prepare: filter databases before show table status (#324)

[ti-chi-bot]

This is an automated cherry-pick of #324

What problem does this PR solve?

In #305, we have switched the method to get table info to SHOW TABLE STATUS. To reduce the access to databases, we'd better filter databases before we executing SHOW TABLE STATUS.

What is changed and how it works?

Filter databases before SHOW TABLE STATUS through conf.Filter.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
  Dump databases and check the log. The databases are filtered before SHOW TABLE STATUS.

Related changes

• Need to cherry-pick to the release branch

Release note

• No release note

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Ehco1996

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[lichunzhu]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 9cc9170