dflib-jdbc: TableSaver to create target table if missing

[andrus]

TableSaver should optionally create the target table if it is missing. There are a few challenges to solve here:

• DDL for table creation is often DB-specific (particularly column types, such as dates, times, etc)
• We don't have a robust API to determine the type of each column in the DataFrame. A "brute-force" implementation will require scanning every cell, and coming up with the JDBC type that would accumulate all values in a given column.
• Determining proper length of VARCHAR / VARBINARY

As a quick workaround we need an API for the caller to provide desired column definitions in the target DB format. Long-term we'll need DB-specific JdbcConnector and better DF type introspection facilities.