Move Flink external transform dependencies into base job server project

[damccorm]

For convenience, the job server project bundles the expansion server. The Flink job server which makes use of the job server project includes additional runtime dependencies to be able to expand external transforms like Kafka and PubSub. Those dependencies should really be present in the base job server project, such that all runner job servers can make use of external transforms.

Imported from Jira BEAM-10386. Original Jira may contain additional context.
Reported by: mxm.