feat: remove all databases in proxy before restore

[mlycore]

Type of change:

• [ ] Bugfix
• [x] New feature provided
• [ ] Improve performance
• [ ] Backport patches

What this PR does / why we need it:

Remove all existing databases in ShardingSphere Proxy before executing pitr restore.

Pre-submission checklist:

• [ ] Did you explain what problem does this PR solve? Or what new features have been added?
• [x] Have you added corresponding test cases?
• [ ] Have you modified the corresponding document?

[sonarcloud[bot]]

Quality Gate passed

Kudos, no new issues were introduced!

0 New issues
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud