Introduce a flink-table-common module

Because more and more table factories for connectors and formats are added and external catalog support is also on the horizon, flink-table becomes a dependency for many Flink modules. Since flink-table is implemented in Scala it requires other modules to be suffixes with Scala prefixes. However, as we have learned in the past, Scala code is hard to maintain which is why our long-term goal is to avoid Scala/Scala dependencies.

Therefore we propose a new module flink-table-common that contains interfaces between flink-table and other modules. This module is implemented in Java and should contain minimal (or better no) external dependencies.