Promote Outbox SMT to GA

The outbox routing SMT is widely used in the Debezium community and has matured over the last year or so. It should be ready for inclusion into the downstream product.

Open questions / to-dos:

• Misc. wording adjustments, don't show byte buffer converter in downstream docs (ENG) (https://github.com/debezium/debezium/pull/2639)
• Why is there table.field.event.key and table.field.event.payload.id? Can we get rid of the latter? If so, deprecate it (the same outcome can be achieved using the generic fields mechanism); don't show it in downstream docs (ENG)
• Hyper-link references between options in the options table (DOC)
• Rename debezium.op.invalid.behavior into table.op.invalid.behavior and change its group; deprecate old name upstream, don't show it downstream (ENG)
• Test without tracing libs present (QE)
• Additional field handling should be unified across all the Debezium SMTs; we'll revisit this for Debezium 2.0 (DBZ-3899)