fix(engine): verify all databases to restore (#425)

Description

Verify connection and content (extensions, locales) of all databases mentioned in the list to restore

Related issue

#425 (closed)

Examples

POST /admin/test-db-source

{
    "dbname": "postgres",
    "host": "172.17.0.2",
    "port": "5432",
    "username": "postgres"
}

or (in case of the database list is not empty)

{
    "dbname": "postgres",
    "host": "172.17.0.2",
    "port": "5432",
    "username": "postgres",
    "db_list": ["postgres", "test"]
}

Checklist

• MR description has been reviewed
• MR changes are functionally tested
• MR does NOT have text changes OR there are text changes and they have been reviewed
• MR does NOT have API/CLI changes OR there are API/CLI changes and they have been reviewed
• MR does NOT have UI changes OR there are UI changes and they have been reviewed

Closes #425 (closed)