Remove `delimited_payload_filter` and add to migration assistant

[cbuescher]

This is a follow up to #26625. What seems left to do is remove the deprecated use of delimited_payload_filter in 7.0, but still allow the old form for indices created in 6.x. Also, a check should be added to the migration assistant.

[romseygeek]

@elastic/es-search-aggs

[cbuescher]

Closed by #27705