Add filter/encode support in header mapper

[onobc]

This is a follow on to 0458f01 that handles the following:

• add support for complex header types (see DefaultKafkaHeaderMapper for inspiration)
• add support for filtering what headers are considered (see DefaultKafkaHeaderMapper for inspiration)
• add support for possible different filter/encode default config between listener/binder
• add support for auto-configured mapper (currently hardcoded in listener and binder configured in binder)
• add docs for this area

[onobc]

Complete via multiple referenced commits.