Manage all the source and sink configurations in Flink ConfigOptions

[crazyzhou]

Problem description
It could be better if we have a central place to store all the client configurations, but now we are separating them in each of the source/sink builder.
This is not an ideal way because these configurations are not clearly exposed to the end users.

Now in order not to break the compatibility, we could keep the legacy source and sink unchanged, but enhance our new source and sink inplementation to use the new config system.

Problem location
New source and sink

Suggestions for an improvement